Proceedings Volume 4876

Opto-Ireland 2002: Optics and Photonics Technologies and Applications

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Proceedings Volume 4876

Opto-Ireland 2002: Optics and Photonics Technologies and Applications

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Volume Details

Date Published: 18 March 2003
Contents: 26 Sessions, 154 Papers, 0 Presentations
Conference: OPTO Ireland 2002
Volume Number: 4876

Table of Contents

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Table of Contents

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  • Session 1
  • Session 2
  • Session 3
  • Poster Session
  • Session 28
  • Semiconductor Devices I
  • Semiconductor Devices II
  • Microcavity Strutures
  • Optical Networks I
  • Optical Networks II
  • Fiber/Waveguides I
  • Fiber/Waveguides II
  • Poster Session
  • Session 13
  • Poster Session
  • Session 15
  • Session 16
  • Session 17
  • Poster Session
  • Session 19
  • Session 20
  • Session 21
  • Poster Session
  • Session 19
  • Poster Session
  • Session 23
  • Poster Session
  • Session 24
  • Session 25
  • Poster Session
  • Session 24
  • Poster Session
  • Session 27
  • Session 28
  • Session 29
  • Poster Session
  • Session 31
  • Poster Session
  • Session 24
  • Case Studies and Panel Discussion
  • Poster Session
Session 1
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Novel imaging in confocal microscopy
We present a description of our work in recent years on imaging in confocal microscopy in the context of biological applications. The first system presented considers a Nipkow disc type arrangement where a detailed investigation of optimal aperture arrangements and spacings is performed. The effect of varying these parameters on the optical sectioning characteristics and on the light throughput is evaluated. Novel routes to achieving alternative multi-aperture configurations are presented. A programmable array microscope demonstrator is described using a ferroelectric liquid crystal SLM. A novel system is also proposed which uses variable focus microlenses in a confocal imaging system. We also discuss current trends in confocal microscopy in biology.
Cell growth on surface-modified medical polymers
Richard J. Sherlock, Daphne N. Bhogal, Michael Ball, et al.
Cellular reactions to implantable medical devices are dominated by the surface properties of materials from which the device is constructed. Consequently, in recent times much effort has been expended on modifying material surface properties to control bioactivity. We examine the effect of exposing surfaces to ultra-violet (UV) light from excimer lasers (λ = 193nm) in a room air environment. Working below the threshold of ablation, samples of nylon-12 and PET were treated. Physical and chemical studies of the surfaces following treatment demonstrated an increase in sample hydrophilicity, though no significant increases in roughness were recorded. Spectroscopic analyses revealed increased oxygen content in the surface layers while there were no chemical alterations in the bulk material. The assessment of in vitro interactions concerning the polymer samples and 3T3 fibroblast cells was conducted using cell counting, viability assays and a confocal microscopic analysis of cytoskeletal fluorescent staining. Results from cell counting and the viability tests confirmed that, subsequent to treatment, there was an increase in cell population on the surface, while improved spreading and activity was observed by confocal microscopy.
Raman spectroscopic analysis of ionization processes in biological systems
Jennifer Conroy, Eoghan O. Faolain, Carmel Mothersill, et al.
Raman spectroscopy was employed to spectroscopically fingerprint the range of animo acids, purines and pyramidines. Irradiation of these components by 10 Gray gamma rays shows that several of the amino acids and pyrimidines are particularly prone to molecular degradation. The spectroscopic signature of the degradation is utilized to identify the molecular origin of the degradation observed in the various biological macromolecules. Irradiation in solution compared to solid sate is employed in an effort to differentiate between primary and secondary ionization processes.
Analysis of the color rendition of flexible endoscopes
Edward M. Murphy, Francis J. Hegarty, Barry P. McMahon, et al.
Endoscopes are imaging devices routinely used for the diagnosis of disease within the human digestive tract. Light is transmitted into the body cavity via incoherent fibreoptic bundles and is controlled by a light feedback system. Fibreoptic endoscopes use coherent fibreoptic bundles to provide the clinician with an image. It is also possible to couple fibreoptic endoscopes to a clip-on video camera. Video endoscopes consist of a small CCD camera, which is inserted into gastrointestinal tract, and associated image processor to convert the signal to analogue RGB video signals. Images from both types of endoscope are displayed on standard video monitors. Diagnosis is dependent upon being able to determine changes in the structure and colour of tissues and biological fluids, and therefore is dependent upon the ability of the endoscope to reproduce the colour of these tissues and fluids with fidelity. This study investigates the colour reproduction of flexible optical and video endoscopes. Fibreoptic and video endoscopes alter image colour characteristics in different ways. The colour rendition of fibreoptic endoscopes was assessed by coupling them to a video camera and applying video colorimetric techniques. These techniques were then used on video endoscopes to assess how the colour rendition of video endoscopes compared with that of optical endoscopes. In both cases results were obtained at fixed illumination settings. Video endoscopes were then assessed with varying levels of illumination. Initial results show that at constant luminance endoscopy systems introduce non-linear shifts in colour. Techniques for examining how this colour shift varies with illumination intensity were developed and both methodology and results will be presented. We conclude that more rigorous quality assurance is required to reduce colour error and are developing calibration procedures applicable to medical endoscopes.
Session 2
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Temporal anisotropy in chlorophyll b solution induced by high-intensity laser pulses
Shu Mei Wang, Li Sun
This paper reports investigation on time-dependant transmittance of Chl b on nanosecond and picosecond time scale. Temporal anisotropy in Chl b solution were observed by streak camera. The transmitted TEM00 mode pumped light was distorted by Chl b solution. The distortion may originate from the temporal anisotropy in Chl b solution induced by the high intensity laser pulses. The state of the temporal anisotorpy was contiued and piled up owing to accumulation of the triplet state within the succeeding pulses in the Chl b solution.
A novel flip-chipped integrated single photon detection platform for proteomics
J. Carlton Jackson, Jonathan West, Aoife M. Moloney, et al.
Novel integrated sensors will be required for future detection platforms for the measurement of fluorescence and luminescence. The current trend towards integration of optical detectors and the broad advances in optical emitting dyes and proteins will be combined in robust, low-cost, point-of-use, diagnostic equipment. To this end we are experimenting with an integrated optical hybrid sensing device which will combine a flip-chipped, array of solid-state single photon counting detectors with surface mount passive quench circuits on a conventional glass substrate. This flip-chipped arrangement both 1) increases the speed of response of the detector and 2) increases the robustness and ease of integration and reduces single photon detector handling requirements. The potential of integrated solid-state photon detectors will be demonstrated for the real-time quantitative detection of luciferase, a light emitting protein expression reporter molecule. A 15μm solid-state Geiger-mode avalanche photodiode (APD) operating in single photon counting mode will be compared with a standard photomultiplier tube (PMT) for luciferase luminescence detection. Detection levels of 2×106 and 1×107 enzyme molecules will be demonstrated for PMT and Geiger-mode APD respectively. The size of the Geiger-mode APD active area will be shown to be the limiting factor in luciferase signal detection for non-integrated applications. A simple geometric model will show that detection limits of 1×104 are achievable in integrated sensing platforms using room temperature operated single photon counting detectors.
Development of an image receptor for use in digital mammography
Mark J. Foley, Philip W. Walton, Wilhelm J. M. van der Putten
We have recently developed a digital x-ray image receptor for use in mammographic procedures. The detector is based upon a photoconductor, amorphous selenium (a-Se), coupled to a polymer dispersed liquid crystal (PDLC) layer. A potential is applied across the structure to create a bias electric field in the photoconductor. When x-rays are absorbed in the photoconductor, electron-hole pairs are released. The created charges are swept to the a-Se /PDLC interface via the applied electric field, which causes potential variations across the PDLC. These variations lead to liquid crystal (LC) molecule re-orientation, which affects the propagation of readout light from an external source through the display. The readout light can be bright in this arrangement so that no secondary quantum sinks are present. Since this system is independent of light creation in contrast with a phosphor screen system, the image brightness can be adjusted independently of the number of x-rays used to make the image. The image can be digitized with a CCD camera and a frame grabber. Results will be presented on the PDLC characteristics, the system model and initial images from the detector.
Session 3
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Development of action levels for MED/MPD skin-testing units in ultraviolet phototherapy
Una M. O'Connor, Neil J. O'Hare
Ultraviolet (UV) Phototherapy is commonly used for treatment of skin diseases such as psoriasis and eczema. Treatment is carried out using UV phototherapy units, exposing all or part of the body for a certain exposure time. Prior to exposure in treatment units, an unaffected area of skin may be tested using UV skin-testing units in order to determine a suitable treatment regime. The exposure time at which barely perceptible erythema has developed is known as the Minimal Erythemal Dose (MED) for UVB therapy and Minimal Phototoxic Dose (MPD) for UVA therapy. This is used to determine the starting dose in the treatment regime. The presence of 'hotspots' and 'coldspots' in UV skin-testing units can result in inaccurate determination of MED/MPD. This could give rise to severe burns during treatment, or in a sub-optimal dose regime being used. Quality assurance protocols for UV phototherapy equipment have recently been developed and these protocols have highlighted the need for action levels for skin-testing units. An action level is a reference value, which is used to determine whether the difference in irradiance output level across a UV unit is acceptable. Current methodologies for skin-testing in Ireland have been characterised and errors introduced during testing have been estimated. Action levels have been developed based on analysis of errors and requirements of skin-testing.
Development of an optical waveguide cantilever scanner
Wei-Chih Wang, Mark Fauver, Joe Nhut Ho, et al.
Design, fabrication, and testing of a micromachined cantilever beam that is optically transmissive and mechanically resonant is presented with application as a micro-optical scanner. An optical waveguide is formed from a 2.2μm thick SiO2 layer deposited on a single crystal silicon wafer and etched to yield a SiO2/Si composite slab cantilever. Using a novel capacitively-coupled reactive ion etching technique, a cavity is back-etched in the silicon to release the 30-40μm thick and 0.5-1.5 mm long cantilevers from the wafer. An etch rate of 2.0-2.2μm/min in Si, an anisotropy of 0.5 and selectivity to thermal oxide (Si: SiO2 = 10:1) and to photoresist (Si: +PR = 8.6:1) are reported. Evaporated aluminum film is used as a passivation material. Optical and mechanical tests are performed on these microfabricated structures. The first mode resonances are found between 16-52 kHz with response amplitudes ranging from 80 to 420 mm. Optical throughput is visible, but greatly diminished due to scattering losses, primarily at the edges of the waveguide. Since cantilever waveguides with resonant frequencies above 20 kHz are potentially suitable for video rate scanning, these devices may be used for image acquisition and display.
Poster Session
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Potential of Raman spectroscopy for the molecular characterization of human tumors
Eoghan O. Faolain, Jennifer Conroy, Mary Hunter, et al.
In this study Raman spectroscopy was employed distinguish between normal and abnormal human tissue. Raman spectra were obtained using a confocal Raman microspectrometer and a laser excitation of 514.532nm for a number of healthy tissues (Tonsil and Cervix) as well as for their diseased counterparts. Each tissue type was classified and its various spectral components were associated with vibrations, rotations etc. of the chemical bonds in the tissues' constituent components. Raman bands have been attributed to biological compounds such as proteins, lipids and DNA as well as to chemical bonds within these compounds such as, C=O stretch in Amide I (1645-1680 cm-1), NH bending in Amide III (1230-1310 cm-1), phenyl ring in Phenylalanine (1004 cm-1). Changes in the relative intensities, position, and width of these bands relate to the composition of the sample. Differences between healthy and diseased tissue with progression to malignancy have been identified and include; an increase in intensity of the phenylalanine ring breathing band (1004 cm-1), the C-C stretch of proteins (1082 cm-1), Amide I band (1655 cm-1) and the C-N stretching modes of proteins (1082cm-1). Decreases in relative intensities were also observed, and include a decrease in intensity of the CH2 deformation (1295 cm-1), CH2 bending of proteins and lipids (1445 cm-1), and the C=O stretching of proteins (1695 cm-1). The molecular origin of the observed spectral changes is discussed.
Ultrafast transient absorption studies of ruthenium and rhenium dipyridophenazine complexes bound to DNA and polynucleotides
Caitriona M. Creely, John M. Kelly, M. M. Feeney, et al.
We report on ultrafast pump and probe studies of biological systems, in the form of polynucleotide and calf thymus DNA complexes. Molecules for study are bound to the polynucleotides and probed in the visible region to observe changes in the absorption over time. Various dipyridophenazine metal complexes are studied alone and complexed with DNA or synthetic polynucleotides to investigate changes occurring in their excited states upon interacting with nucleobases. Transient absorption measurements are performed pumping at 400nm and probing from 450-700nm with pulse duration of 400fs.
Research on refractive index distribution in biological tissues
From the view of refractive index distribution, biological tissue can be regarded as a refractive index random media. Inhomogeneous distribution of refractive index is the physical basis of the high scattering property of biological tissue, whose scale is close to wavelength. Disperse scatter model and statistical distribution function are introdcued to describe the refractive index distribution in biological tissues such as blood tissue. Based on the disperse scatter model and scatter theory, the relations between refractive index fluctuation and scattering coefficient of biological tissue are derived and corresponding formulas are given to calculate the refractive index fluctuation in biological tissue. The formulas are applied to calculate the refractive index distribution of blood tissue in different status, combining the Rayleigh scattering describing the single scattering events. The calculating results are illustrated in the paper.
Time-gated fluorescence imaging of chloroaluminum phthalocyanine tetrasulfonate in a tissue phantom
Sarah L. Gundy, Wilhelm J. M. van der Putten, Andrew Shearer, et al.
Phthalocyanine derivatives are currently under investigation for use in Photodynamic Therapy, which is a promising treatment for cancer. These materials, which display preferential uptake in cancerous cells, also exhibit high fluorescence yields, and can be used for tumour detection. Problems with steady-state fluorescence techniques such as background autofluorescence can be eliminated by the use of time-resolved techniques. Improved contrast can be obtained with time-resolved techniques because of the differing lifetimes between endogenous and exogenous photosensitisers. An imaging system was constructed using a fast (200 psec) gated CCD camera and a pulsed 635 nm laser diode. A tissue phantom was assembled to test the system by drilling thirty-six wells of varying diameter and depth (10 mm to 1 mm) into a block of polymethyl methacrylate (PMMA). The system was used to record images of chloroaluminum phthalocyanine tetrasulfonate within the wells at differing concentrations in phosphate buffer. A mixture of 1) Intralipid to mimic tissue scatter, 2) Evans blue to mimic tissue absorption, and 3) zinc phthalocyanine tetrasulfonate to mimic healthy tissue autofluorescence of varying depth was placed on top of the PMMA block. These results contribute to the precision of a time-gated imaging system to image living organisms using fluorescence lifetimes.
Session 28
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Luminescence properties of coumarins and quinones
An extensive analysis of the Raman and IR spectra of laser dyes like Coumarins and Quinones derivatives has been performed, based on a reanalysis of vibrational spectrum of Polycyclic aromatic hydrocarbons anthracene and naphthalene. Raman and FTIR techniques are used to assign the vibrational modes of Coumarin, Coumarin 480 and Coumarin 540A and 1,4 benzoquinone molecules. Vibrational modes of substituted coumarin dyes are investigated for the first time in powder form using Raman spectroscopy.
Semiconductor Devices I
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Far-infrared (THz) electroluminescence from Si/SiGe quantum cascade heterostructures
Stephen A. Lynch, Douglas J. Paul, Robert Bates, et al.
There is strong interest in the development of sources that emit radiation in the far infrared (1-10 THz) frequency range for applications which include early detection of skin cancer, dental imaging, telecommunications, security scanning, gas sensing, astronomy, molecular spectroscopy, and the possible detection of biological weapons. While a number of THz sources are available, there are at present no compact, efficient, cheap and practical high-power solid-state sources such as light emitting diodes or lasers. Silicon is an excellent candidate for such a THz source since the lack of polar optical phonon scattering makes it an inherently low loss material at these frequencies. Furthermore, since over 97% of all microelectronics is presently silicon based, the realisation of a silicon based emitter/laser could potentially allow integration with conventional silicon-based microelectronics. In this paper THz electroluminescence from a Si/SiGe quantum cascade structure operating significantly above liquid helium temperatures is demonstrated. Fourier transform infrared spectroscopy was performed using step scan spectrometer with a liquid helium cooled Si-bolometer for detection. Spectra are presented demonstrating intersubband electroluminescence at a number of different frequencies. These spectral features agree very well with the theoretically calculated intersubband transitions predicted for the structure.
Economic single-mode lasers for WDM
Christopher Percival, Paul Lambkin, J. Kando, et al.
Development of a cheap and simple laser which has narrow linewidth, suppressed sidemodes, is insensitive to temperature change and which can be easily fabricated at a range of wavelengths from a single wafer is one of the most sought after goals of optical communications for Wavelength Division Multiplexing. Toward such a device we have produced edge-emitting Fabry-Perot cavity lasers that have waveguide perturbations that modulate the output cavity mode spectra. The suppression of the cavity modes is a function of the geometry and positioning of the perturbations, therefore emission wavelength is insensitive to device temperature. Single mode operation is easily achieved with only three perturbations defined by standard optical lithography. Arrays of devices from a single chip display ranges of emission wavelengths, suggesting possible future applications to optical communications. Modelling using an optical field transfer matrix model indicates that this is not a reflectivity-controlled process, as for DBR structures, but rather a loss process that suppresses unwanted cavity modes. Fourier transforms of emission spectra display features corresponding to the waveguide perturbations and are being utilised as a design tool to select peak emission wavelength.
Effects of laser diode nonlinearities in hybrid fiber/radio systems
With the increasing demand for broadband services, it is expected that hybrid fiber/radio systems may be employed to provide high capacity access networks for both mobile and fixed users. Third generation (3G) mobile systems for example, will operate around the 2.4Ghz band, while fourth generation (4G) systems may operate in the 5.8GHz band or beyond. To make these future generation systems commercially viable it is important to keep costs as low as possible. One method of keeping costs to a minimum is to have a central station (CS) where the radio frequency (RF) data signals are modulated onto an optical carrier and sent to a number of base stations (BS) over optical fiber, before being transmitted over air to the users. This allows the BS complexity to be kept to a minimum. A possible solution for generating the optical RF data signals for distribution over fiber is to directly modulate the RF signal onto an optical carrier using a laser diode. The major problem with this technique is that broadband microwave systems are likely to use frequency division multiplexing for transmitting very high data rates. This will thus involve modulating the laser with electrical data signals at multiple frequencies, which will result in serious interference due to dynamic nonlinearities in standard laser diodes around the electrical transmission frequencies. This distortion, known as intermodulation distortion (IMD), can significantly degrade the performance of optically fed microwave systems for high-speed access networks. This paper examines how this laser nonlinearity degrades the performance of hybrid fiber/radio systems operating in various RF transmission bands, and investigates possible techniques to overcome these problems.
Semiconductor Devices II
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Nanowire array electrode structure for organic light-emitting diodes
Organic light emitting diodes were fabricated using a novel electrode structure. The anode structure comprised of a metallic nanowire array and was fabricated by electroplating porous aluminium oxide with copper. These devices were compared with devices with a conventional planar anode structure. The light emitting polymer Poly[(4-methylphenyl) imino-4,4'-diphenylene-(4-methylphenyl)imino-1,4-phenylene-ethenylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-ethenylene-1,4-phenylene)] was used as the emissive material in single layer devices of structure Cu: TPD(4M)-MEH-PPV: Al, where the aluminium was negatively biased with respect to the copper. The DC current-voltage characteristics of both device types are presented. The electroluminescence spectra are also presented. We found that due to the reduction in active area in the nanowire device from that of the planar device the current density reached in the nanowire array anode device exceeded that in the planar anode device by a factor of eight. Similarly a relative increase in the electroluminescence intensity was also observed.
Microcavity Strutures
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Red and green resonant cavity LEDs for datacom applications
Brian Corbett, Brendan J. Roycroft, Alistair Phillips, et al.
We report on the development of resonant cavity LEDs (RCLEDs) for use in short distance datacommunication applications using the IEEE 1394 standard where plastic optical fibre (POF) is the physical medium. The devices are designed for 650nm and 500nm emission where POF has low attenuation. The red devices based on InGaAlP/GaAs are optimised for room temperature operation and 90μm diameter devices have a maximum coupled power to 1mm diameter POF of 1mW. At 10mA the coupled power is 0.4mW with a quantum efficiency of 2%. Current spreading is shown to be critical in optimising the output power. The devices function as resonant cavity detectors with a response FWHM of 4.2nm centred at 650nm. The blue-green RCLEDs are based on InGaN/GaN and use a hybrid metal-epitaxial mirror cavity. This wavelength is preferable for longer links. The substrate emitting devices have fibre-coupled powers of 200μW at 20mA. A datarate of 250Mb/s is measured. The resonant cavity is confirmed by angularly resolved spectral measurements. The tradeoff between green and red devices is discussed.
Optical design of GaN resonant cavity LEDs emitting at 510-nm for use in plastic optical fiber applications
The optimized optical design of GaN resonant cavity light emitting didoes (RCLEDs) emitting at 510nm for maximum extraction efficiency into numerical apertures (NAs) of 1.0 (total emission) and 0.5 (typical plastic optical fiber NA) are determined using a modeling tool based on the simulation of dipole emission in a multilayer structure. The optimization is performed for a metal-AlGaN/GaN DBR cavity structure as functions of the aluminum fraction in the DBR and the internal quantum well (QW) emission linewidth. The optimum number of DBR pairs is shown to depend on both these parameters together and the emission NA, and varies between 3 and 14. The maximum calculated extraction efficiency for a metal-AlN/GaN cavity structure, assuming a QW emission linewidth of 30nm, is 0.18 (0.055) into an emission NA of 1.0 (0.5). The position of the QW relative to the metal mirror is shown to be the crucial device parameter in determining the extraction efficiency of the RCLED. Simulations show farfield measurements should provide information on the position of the QWs in the cavity. The reduction in the spectral emission linewidth of the RCLED due to the cavity is also modeled.
FTIR and Raman investigation of vertically etched silicon as a 1D photonic crystal
The reflection spectra of composite materials on the base of grooved silicon and grooved silicon infiltrated with nematic liquid crystal (LC) have been calculated using the optimal parameters of a grooved silicon matrix suitable for the infrared range. The grooved silicon structures with different lattice constants (A=16, 12, 8 and 4 mm) have been designed and prepared. An important parameter of these structures is the thickness of the silicon walls (DSi). This has been obtained using simulations of the spectra. This parameter was used for further analysis of the spectra of composite material grooved Si-LC. The experimental reflection is reaching of 65% in maximum (with signal modulation from maximum to minimum up to 55%) for the composite structures with a small number of lattice periods that makes these structures very perspective with a potential applications. The analysis of the polarised infrared spectra of Si structures infiltrated with LC allows one to determine the orientation and the refractive index (NLC) of the liquid crystal. For the samples with a distance between Si walls of 6-10 mm, it was found that the refractive index was NLC=~ 1.5 for polarised light and NLC 1.5 for s-polarised light. This leads to the conclusion on the planar orientation of liquid crystal molecules with respect to the Si walls. For the samples with distance between Si walls less than 3 mm, a homeotropic alignment of liquid crystal molecules has been found. Micro-Raman spectroscopy has been applied for analysis of stress in such Si structures. The maximum stress of about 2 GPa was obtained on the top of Si walls (under Si dioxide layer).
Optical Networks I
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Ultrafast optics for broadband photonic communication systems
The ever-increasing demand for bandwidth in telecommunication networks is accelerating the use of optical fibre for broadband communication systems. In order to continue to increase the data rate of single channel optical communication systems, it is anticipated that Optical Time Division Multiplexing (OTDM) techniques will be used in future photonic systems. OTDM technologies should allow the transmission of information at data rates in excess of 100 Gb/s on a single wavelength, and by employing OTDM in conjunction with Wavelength Division Multiplexing (WDM), it should be possible to develop highly flexible, and spectrally efficient, multi-terabit/s optical networks. An essential element of any OTDM system will be the generation of sub-picosecond pulses to represent the data. The temporal and spectral purity of the optical pulses at the transmitter will essentially determine the overall data rate that can be achieved. In order to provide the multi-terabit/s data rates required, these pulses must be compressed into the pico- and sub-picosecond range. This paper will look in greater detail at this key element involved in an all-optical time division multiplexed system, namely the generation of sub-picosecond optical pulses, and it will explore the type of system performance that can be achieved given the spectral and temporal purity of the optical pulses.
Hybrid radio/fiber system employing SCM for the distribution of multiple RF carriers with a directly modulated laser transmitter
The authors present the idea of using direct modulation of a laser for generating multiple RF carriers for hybrid radio/fiber systems. External light injection is used in order to increase the modulation bandwidth of the laser and at the same time to improve the overall system operation. The experiments show a 16 dB enhancement in the performance of the system used for distributing 155 Mb/s data signals on 18.6 and 19 GHz carriers.
Optical Networks II
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Performance issues associated with WDM optical systems using self-seeded gain-switched pulse sources
It is obvious that the development of a wavelength tunable source of short optical pulses will be of paramount importance for future Wavelength Division Multiplexing (WDM), optical time division multiplexed (OTDM), and hybrid WDM/OTDM optical communication systems. Self-seeding of a gain-switched Fabry-Perot (FP) laser is one of the most reliable techniques available to generate wavelength tunable optical pulses. An important characteristic of these self-seeded gain-switched (SSGS) sources is the variation in the side-mode-suppression-ratio (SMSR) as the wavelength is tuned, as this may ultimately affect their usefulness in optical communication systems. A quantitative analysis of how mode partition noise and side mode suppression ratio affects a wavelength division multiplexed system is investigated here. Bit Error Rate measurements have been carried out on a 4-channel wavelength division multiplexed set-up using tunable self-seeded gain-switched pulse sources. These measurements demonstrate the degradation in overall system performance, due to mode partition noise, as the side mode suppression ratio of the self-seeded gain-switched optical pulse sources is reduced. The results also show that the constraints on the minimum side mode suppression ratio required increase with the number of channels in the system.
Measurements of optical signal impairments of wavelength division multiplexing systems
Sean O'Duill, Gavin Mulvihill, Yonglin Yu, et al.
This paper investigates the effect that Four Wave Mixing (FWM) has on Frequency Shift Keyed (FSK) optical signals. The paper will show how an optical FSK modulated signal can be implemented using a widely tunable laser. These lasers will have a bigger impact in future optical transmission systems due to their agile wavelength capabilities. Then measurements of FWM in a Semiconductor Optical Amplifier (SOA) and in Zero Dispersion Shifted Fiber (DSF) will be presented. SOAs are of crucial importance in modern & future transmission systems as many operations can be implemented using their highly nonlinear properties, such as wavelength conversion, pulse reshaping & format conversion can be implemented. While Zero DSF is less popular these days, due to its nonlinearities, nevertheless the fiber still forms the core of many networks and thus its ability to handle many different WDM signals without introducing potential interference needs to be investigated.
Actual speed limitations of wavelength switching for optical networks
Gavin Mulvihill, Yonglin Yu, Sean O'Duill, et al.
Due to the continuous growth of data traffic current telecommunications systems are being pushed to the extremes of their capacity. Bottlenecks are particularly evident at the routers, where optical to electrical conversion must take place to read the routing information. Using optical only routing, traffic flow would be much more streamlined. Central to this optical routing is the tunable laser, the speed of the routing is obviously dependent on the speed at which the laser can switch between different wavelengths. Wavelength switching is achieved through the application of currents to the front, back and phase sections of the laser. With each change in current there is a corresponding change in the temperature of the laser. It is extremely important to quantify and minimise the temperature effects for stable accurate wavelength output. A measurement rig which had been previously used for high speed switching has been setup under labview control to study these transients. The laser is tuned to a wavelength and then is switched to another wavelength by applying currents to the three sections quickly. A fabry perot interferometer is used to quickly determine the wavelength of the laser.
Optical switches using electro-optical effects in liquid crystals
Yuliya Semenova, Sergey M. Dovgalets, Yuri Panarin, et al.
Optical switches using two electro-optical effects in liquid crystals are proposed and investigated for incorporation in a switch matrix for optical networks. These two devices employ selective reflection in cholesteric layers and total reflection at the border between glass and nematic liquid crystal. Prototypes of these switches have been designed and their parameters have been investigated. Initial results show the switching contrast ratio of 38,5 and 42 dB, respectively, with insertion loss about 2.3.2.9 dB for polarized light.
Full-coverage microsecond wavelength switching of a monolithic widely tunable laser, from any channel to any channel, over the entire C band on the ITU G.682 ITU grid
Tommy Mullane, David McDonald, Tom Farrell, et al.
Full coverage, wavelength switching over the entire C band on the 100 GHz ITU frequency grid, from any channel to any channel in a single microsecond, is presented here for the first time. This switching time is achieved whilst ensuring that the terminal lasing frequency is within +/- 2.5GHz of the target ITU 1 us after the switching event. The current paper presents the key parameters associated with such a laser transmitter and how these are unaffected by the addition of the wavelength switching functionality, i.e. linewidth, switching time, SMSR and transient frequency error. Next generation networks will move from physical path managed optical networks to logical wavelength managed networks where, efficient utilisation of the network on the wavelength level will be demanded. Fast and robust switching of the wavelengths is a key technological requirement for delivering on this.
Fiber/Waveguides I
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Low-loss splices between different fibers
Conleth Denis Hussey, Kenneth P. Oakley
Dispersion compensating fibre (DCF) and high NA fibre (HNA) can be fusion spliced to standard communications single mode fibre (SMF) with considerably reduced splice losses if the cores on both sides of the splice are adiabatically diffused. Overall losses of 0.2 dB and 0.05 dB for DCF/SMF and HNA/SMF splices, respectively, have been repeatably achieved with this technique. With an alternative adiabatic splice fattening technique, small diameter fibre (80/5.3 mm) can be fusion spliced to standard communications fibre (125/9.5 mm) with losses as low as 0.6 dB.
Melted microlenses: fabrication, performance, and modeling
We present a two part study of melted microlens arrays. This first part concentrates on the production and measurement of microlens arrays while the second part examines attempts to model the microlens profiles. Particular emphasis is placed on the photoresist reflow method of microlens production that was suggested by Popovic et al., as this was the method used to produce the microlens examined in this study. Lenses produced using this method can have large deviations from the spherical case, i.e. the profile that would be expected from a simple minimisation of the surface energy. These deviations have not been explained to date in the literature, however a number of possible causes for this deviation are given in this paper. Therefore the fundamental questions we wish to explore here are: (1) Why physically do dips occur? and (2) Can the resulting surface profile be predicted? Any model developed to quantitatively estimate the optical effects of surface shape will depend on the physical assumptions made regarding the surface formation mechanism. A number of possible causes are listed in this paper. The second part of this study attempts to model microlens surface profiles are discussed. The models used are analytic models. These models are examined for a range of different f numbers, f/#, and used to fit the experimental data discussed. A comparison of the models is made.
Finding Ge-Al-doped fiber parameters for modeling erbium-doped fiber amplifier operation
John A. Ging, Ronan F. O'Dowd
The behaviour of Erbium-Doped Fibre Amplifiers (EDFA) is investigated as a function of basic fibre constituents and length in order to provide sufficient parameters for any modelling of its gain or noise profiles. The efficiency of the amplifier is found to be strongly dependent on the erbium ion concentration, the excited-state lifetime, the overlap integral of the erbium with the optical mode and the absorption and emission cross-sections. For convenience, these factors can then be lumped into two fibre specific parameters, namely the intrinsic saturation, PkIS, and absorption coefficients, ak. The topics addressed in this paper include the calculation of these parameters in order to provide a model for the gain or noise in an EDFA operating in the steady-state regime. Mechanisms that may deplete the gain achievable are identified and it is described how some of these might be overcome by finding the optimum amplifier length to obtain maximum gain. This paper presents comprehensive analysis to be coupled with available numerical and implicit analytical methods and will enable a systematic design and performance study of the EDFA.
Planar optical integrated circuits based on UV-patternable sol-gel technology
Jean-Marc Sabattie, Brian D. MacCraith, Karen Mongey, et al.
Planar lightwave circuits (PLCs) made from photo-patternable sol-gel materials are attracting considerable R&D interest. This is due to the advantages they offer for applications in optical telecommunications and their compatibility with existing silicon technology process equipment. In particular, the ability to produce devices compatible with silica optical fibres using a straightforward, environmentally friendly, photolithographic process is very attractive. The approach is now well-established in the literature and typically involves the incorporation of an acrylate moiety in the sol-gel precursor mixture, thereby providing a photo-polymerisability function. In this work, we report on the fabrication of passive optical components and devices designed for datacomms applications using visible diode lasers or the 1st telecom window. Silica-based sol-gel waveguides have been integrated in an opto-electronic multichip module (OE-MCM) demonstrator for optical interconnect applications. We have fabricated an 8-channel transmitter module for parallel optical interconnects (POI) based on 2 sub-modules: (a) an optical interface sub-assembly based on photo-patterned sol-gel optical waveguides, and (b) an optoelectronic component sub-module comprising an array of VCSELs. We describe here the fabrication, characterization and performance of the optical components and a POI Transmitter chip.
Fiber/Waveguides II
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Transfer-matrix-based simulation of fiber Bragg gratings for ITU DWDM optical networks
Fionan Mc Grath, Ronan F. O'Dowd
With the need for high capacity optical wavelength division multiplexing systems growing, the importance of filters to rout the signals is huge. Fiber Bragg gratings play a huge part in the filtering of signals, such as in add-drop multiplexers. In order to design communication networks, there must exist an accurate simulation package to solve the complex differential equations that govern light propagation within the fiber. Using the transfer matrix method, where the matrices for individual sections are defined using methods proposed after analysis of the grating as a periodic crystal structure gives a close approximation to the solutions of these equations. Transfer matrices must be defined for a variety of different sections in both uniform and non-uniform gratings and the overall result obtained by cascading a large number of such sections. Problems exist with the inclusion of such features as chirp and apodization, which vary upon penetration into and out of the grating. Obtaining key values from the solutions, such as reflectivity and bandwidth of the spectrum of a grating in a simulation environment will lead to a faster and better design for DWDM filters. Since no environment is perfect research into strain and temperature effects of gratings is included.
Inscription of long-period fiber gratings by femtosecond UV radiation
Adrian Dragomir, David N. Nikogosyan, Konstantin A. Zagorul'ko, et al.
Using a new automated set-up and high-intensity 264 nm radiation, we record long-period fiber gratings with strong attenuation peaks in different fibers. The effects of laser inteisty and/or fluence in both H2-loaded and H2-outdiffused fibers aer investigated.
Characterization of the effects of different lasers on the tensile strength of fibers during laser writing of fiber Bragg gratings
Fibre Bragg gratings (FBGs) continue to be used in a wide variety of different telecommunications products such as filters, pump stabilisers and dispersion compensators. The increased specifications being demanded by successive generations of FBG components mean that higher manufacturing controls are needed to ensure high quality performance. One of the key areas of concern has been the effect of the laser exposure on the tensile strength of the fibre, since this affects yield, quality and lifetime of the FBG device. No comparative study has, to the best of our knowledge, so far been conducted to measure the relative merits of different exposure conditions. We present measurements of the degradation of the strengths of Corning SMF28 and intrinsically photosensitive fibres from laser exposure with the following lasers: excimer lasers at 193nm and 248nm and argon-ion laser at 244nm. A comparison is presented of the fibre pull strengths under varying illumination conditions with the different laser systems and a methodology established for favourable exposure conditions for FBG writing with reduced fibre strength degradation.
Poster Session
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Light amplification and lasing in doped polymer optical fibers
Takeyuki Kobayashi, Werner J. Blau, Hartwig Tillmann, et al.
We report on a large optical gain, over the wide spectral range, and lasing in a glass-clad polymer optical fiber that uses a novel highly fluorescent stilbenoid compound, 1,4-bis(4-diphenylamino-styryl)-benzene. The compound has a high quantum yield of 0.85 in polystyrene and a large Stokes shift of about 80 nm. A fiber doped with 0.2-wt. % of the compound is photoexcited with a thin striped shape area at 355 nm with nanosecond optical pulses, and the emission from one end is monitored as a function of the excitation length to deduce the net gain coefficient. The gain spectroscopy has revealed a broad optical gain exceeding 25 cm-1 and up to 36 cm-1 at 494 nm that covers a spectral range of about 70 nm when the fiber is transversely photoexcited at 12 mJ/cm2. The large gain has been utilized to demonstrate blue laser emission at 489 nm from the fiber (which is only 1.4 cm in length) in a low finesse cavity defined by the Fresnel reflections at the fiber-air interfaces. The threshold for lasing is found to be 1.7 mJ/cm2.
Carbon nanotube composites as efficient charge transport media in organic optoelectronic devices
Patrick Fournet, Jonathan N. Coleman, Diarmuid F. O'Brien, et al.
Thanks to their cheap processability, organic optoelectronic devices are believed to gradually gain a non-negligible place on the market. However, their performances remain low, mainly because of the poor electron transport in conventional polymers used in such devices. Carbon nanotubes, with a bulk conductivity as high as 10E5 S/m, could therefore be seen as potential candidates to address this important issue. In this work, we have studied the use of a carbon nanotube and polymer composite as an active layer in organic light-emitting diodes and organic photovoltaic devices. Enhanced brightness was achieved using the composite as an electron-transport layer in organic light-emitting diodes, the best efficiency being obtained for those devices with a nanotube content of 1.2 %. Secondly, we have studied the use of the polymer and carbon nanotube composite as the active layer in organic photovoltaic cells. Photocurrents in such devices were greater than that of the cells without carbon nanotubes. It is believed that carbon nanotube composites could act as efficient transport media for charges, which were originally dissociated. This study has demonstrated that carbon nanotubes can be used as functional materials in organic optoelectronic devices and enhance the charge transport, hence the efficiency in such devices.
Optical and electrical studies of modified conjugated polymer films
A thin film preparation technique leading to reduced polaron formation in thin films of the polymer poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) (PmPV) was used to prepare thin films with significantly improved photoluminescence efficiency. This was achieved through increased interchain separation in films prepared using this technique. Photoinduced absorption measurements were performed to study the nature of the increased photoluminescence efficiency. The electrical transport properties of PmPV films prepared using this preparation technique were measured using both direct and alternating current measurement techniques and found to be improved for positive charge carriers and unchanged for negative charge carriers relative to conventional preparation techniques. The relative permittivity was shown to be greater in this film type, due to the longer delocalisation lengths resulting from increased interchain separation in these films. Fabrication of single layer light emitting devices utilising PmPV prepared using this technique were found to be significantly brighter and to have longer device operating lifetimes.
Photoluminescence quenching and degradation studies to determine the effect of nanotube inclusions on polymer morphology in conjugated polymer-carbon nanotube composites
The change in morphology of a polymer matrix upon the introduction of carbon nanotubes is characterized in this study. Multi-walled carbon nanotubes were dispersed in the conjugated copolymer poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) (PmPV) to produce a composite material. Photoluminescence (PL) measurements show a reduction in PL efficiency as the nanotube content is increased. Electron microscopy studies have shown an ordering of the polymer around the nanotubes allowing a layer thickness of 25nm to be estimated. This observed thickness agrees well with the expected value of 55nm calculated using a model relating the PL decrease to the changes in conformation that result from polymer - nanotube interactions. Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) techniques have been employed to investigate how the polycrystallinity of the polymer is affected due to the presence of nanotubes. The results indicate an increase in polymer crystallinity occurs due to an interfacial interaction between the polymer and the nanotube.
Electronic transfer studies of fullerene/polymer hybrids
In this study we examine the interaction of both cis and trans poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene (PmPV-co-DOctOPV) with C60 in solution From the presented data it is clear that there is an interaction between the HE PmPV and C60. Just what this interaction is however is not as clear. A possible explanation that fits the available data involves the HE PmPV wrapping around the C60 molecules, similar to the effect observed by Dalton et al with Carbon Nanotubes. In theory the close proximately of the coils to the C60 molecules may allow for charge transfer or energy transfer between to the two molecules. If this theory is correct it would explain the why the absorption spectra of HE-PmPV at the different loaded fraction displays a negative deviation for the expected values. It may be speculated that due to the coiling the C60 molecules are prevented from absorbing photons of light, consequently resulting in a reduction in it's contribution to the overall intensity. This theory would also explain the increased quenching effect observed in the luminescence spectra at the same percentage weights, since the close proximity of the coils to the C60 molecules allows for charge or energy transfer between the two.
Design and fabrication of a waveguiding organic double heterostructure light-emitting device: a milestone in the development of an electrically pumped polymer laser
Colin R. Belton, Eric Toussaere, Hans-Heinrich Hoerhold, et al.
We present measurements of the optical constants of a series of spin cast conjugated polymer and thermally evaporated small molecule films on silicon substrates. The optical constants are measured, using spectroscopic ellipsometry, from 0.75eV up to just below the band-gap of each material. The optical constants are then obtained by fitting a homogeneous Cauchy model to the ellipsometry data. Using this data the waveguiding behaviour of a double hetero-structure device with edge emission is modeled using the well-established Beam Propagation Method (BPM). The waveguide loss of double hetero-structure devices is modeled for different device geometries and across the emission band of an experimentally prepared light emitting, waveguiding double hetero-structure organic device. The emission characteristics of the experimental device compare favourably with results of the simulation based on the measured optical constants. These results have important implications for the design of future electrically pumped organic laser devices.
Theory of the band structure of pentacene organic crystals
Clive Harris, Simon D. Elliott, Eoin P. O'Reilly
We report a systematic investigation of the band structure of pentacene crystals, using both density functional theory (DFT) and a simpler tight-binding (TB) approach. We use the DFT method to determine the equilibrium crystal structure and the band structure along the crystallographic axes. We then introduce an analytic π bonding TB model which fully accounts for the calculated DFT band dispersion. The calculated band widths, effective masses, and their anisotropy are in very good agreement with previous experimental estimates. The band anisotropy in the ab plane and the close similarity between the conduction and valence band dispersion are fully accounted for within the TB model.
Characterization of macroporous silicon for electronic applications
Tatiana S. Perova, Ekaterina V. Astrova, Remy Maurice, et al.
Micro-Raman spectroscopy was used in this study for the analysis of the influence of process conditions on the strain and stress in macro-porous silicon (ma-PS) layers. As expected, it was found that oxidation results in significant wafer bending, depending on the layer porosity. The magnitude of stress of about 0.33 Gpa was found for ma-PS sample with lattice constant of 4 mm while for sample with the lattice constant of 12μm it was only 0.175 GPa. Dissolution of the oxide layer restores the flatness of the samples after the first oxidation. Repetition of the oxidation cycles leads to a 'memory effect', as the residual deformation increases. The results are consistent with results obtained for similar samples using X-ray diffractometry and topography and curvature measurements.
Numerical aperture characteristics of angle-ended plastic optical fiber
With the increasing information rates demanded in consumer, automotive and aeronautical applications, a low cost and high performance physical transmission medium is required. Compared with Silica Optical Fiber, Plastic Optical Fiber (POF) offers an economic solution for a range of high-capacity, short-haul applications in industrial and military environments. Recently, a new type of POF, the perfluorinated graded-index plastic optical fiber (PF GI-POF), has been introduced that has low losses and high bandwidth at the communication wavelengths 850 nm and 1300nm. POF is normally terminated perpendicular to the fiber axis. We propose an angle-ended POF, which is terminated at non-perpendicular angles to the fiber axis. The aim of the research is to investigate the numerical aperture (NA) characteristics of angle-ended POF along the major axis of the elliptical endface. A theoretical model indicates that the NA of the angle-ended POF will increase nonlinearly with tilt-angle and the acceptance cone will be deflected with the angle of the deflection increasing nonlinearly with tilt-angle. We present results for the measured NA and the measured deflection angle using the far-field radiation method. Results are presented for 13 angle-ended SI-POF tilt-angles. We also present results for theoretical value of NA and deflection angle as a function of tilt-angle. The agreement between the measured and theoretical value is good up to tilt-angles of about 15 degrees, beyond which deviation occurs.
Analysis of loss mechanisms in photonic crystal fibers
Ravindra Kumar Sinha, Shailendra Kumar Varshney
Analysis of different loss mechanisms that occurs in photonic crystal fibers (pcfs) is discussed. It is shown that loss appears when these fibers are either joined with another fiber or bent in a radius. The joint losses are obtained for transverse as well as angular misalignments. Peterman spot size definitions are used to define these losses. Bending losses in pcfs are also obtained for different designs of pcfs. It is observed that these loss definitions show dependence on the photonic crystal cladding parameters.
Difference-harmonic generation in quantum dots
Fedir T. Vasko, Eoin P. O'Reilly
We investigate the prospects for difference-harmonic genration due to intersubband transitions in n-doped quantum dots. The third order susceptibility tensor is calculated for flat conic quantum dots, where the lateral size is significantly greater than the height. The energy levels and the dipole matrix elements associated with the intersubband transitions are obtained in the framework of the effective mass approximation, including a simple model for self-consistent screenign in the dots. The spectral dependence of the susceptibility is calculated and the double-resonant enhancement of the response is considered. Numerical estimates of the efficiency of transformation of a two-color near-IR pump indicate that it may be possible to observe a mid-IR output of the order of a millimwatt for the case of a multi-QD-sheet structure placed in the center of a resonator.
Size-selective photoluminescence excitation spectroscopy in CdTe quantum dots
Yury Rakovich, Laura Walsh, Louise Bradley, et al.
We present a photoluminescence and photoluminescence excitation study of CdTe quantum dots, prepared via a novel organometallic approach. The global photoluminescence (excited at the energy above the absorption edge) showed a red shift of 75 meV with respect to the first absorption peak. This band edge emission was found to be strongly dependent on the excitation photon. Resonant emission spectra showed a pronounced spectral shift and line narrowing with decreasing excitation energy. The resonant Stokes shifts were extracted from photoluminescence and photoluminescence excitation data. The minimum magnitude of the resonant Stokes shift of 14 meV was obtained at room temperature.
Large-area Geiger-mode avalanche photodiodes for short-haul plastic optical fiber communication
Large-area Geiger-mode avalanche photodiodes (GMAPs) that are designed to be compatible with a 1.5μm CMOS and silicon-on-insulator (SOI) CMOS process are presented here as candidate detectors for use in optoelectronic integrated circuits (OEICs). The photodetectors have 250μm and 500μm diameter active areas with 20um virtual guard ring overlaps. The GMAPs have a breakdown voltage of -30V and will be biased below breakdown in avalanche mode. The diodes' junction capacitances at 5V reverse bias are 11.66pF and 41.71pF respectively and 4.99pF and 17.95pF respectively at 27V reverse bias. The 250μm photodiode has a calculated bandwidth of 454MHz when biased at -5V while the 500μm diode has a calculated bandwidth of 142MHz when biased at -5V calculated using small-signal equivalent circuits for the devices.
Session 13
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Laser cladding: repairing and manufacturing metal parts and tools
Leo Sexton
Laser cladding is presently used to repair high volume aerospace, automotive, marine, rail or general engineering components where excessive wear has occurred. It can also be used if a one-off high value component is either required or has been accidentally over-machined. The ultimate application of laser cladding is to build components up from nothing, using a laser cladding system and a 3D CAD drawing of the component. It is thus emerging that laser cladding can be classified as a special case of Rapid Prototyping (RP). Up to this point in time RP was seen, and is still seen, as in intermediately step between the design stage of a component and a finished working product. This can now be extended so that laser cladding makes RP a one-stop shop and the finished component is made from tool-steel or some alloy-base material. The marriage of laser cladding with RP is an interesting one and offers an alternative to traditional tool builders, re-manufacturers and injection mould design/repair industries. The aim of this paper is to discuss the emergence of this new technology, along with the transference of the process out of the laboratory and into the industrial workplace and show it is finding its rightful place in the manufacturing/repair sector. It will be shown that it can be used as a cost cutting, strategic material saver and consequently a green technology.
Ablation thresholds in ultrafast laser micromachining of common metals in air
In the current work ablation of metal targets in air with femtosecond laser pulses is studied. The laser pulses used for the study were 775 nm in wavelength, 150 fs in pulse duration and the repetition rate was 100 Hz. Ablation thresholds have been measured for a number of metals including stainless steel niobium, titanium and copper. The ablation depth per pulse was measured for laser pulse fluences ranging from the ablation threshold (of most metals) ~ 0.1 J/cm2 up to 10 J/cm2. It has been shown previously that there are two different ablation regimes. In both cases the ablation depth per pulse depends logarithmically on the laser fluence. While operating in the first ablation regime the ablation rate is low and is dependant on the optical penetration depth, α-1. While in the second ablation regime the ablation rate is greater and is characterized by the 'electron heat diffusion length' or the 'effective heat penetration depth'. In the present study good qualitative agreement in the ablation curve trends was observed with the data of other authors, e.g. Nolte et al (1997).
UV laser micromachining of silicon, indium phosphide, and lithium niobate for telecommunications applications
The laser micromachining characteristics of indium phosphide, lithium niobate and silicon have been characterised using a 355nm neodymium vanadate laser and 193nm and 248nm excimer lasers. Etch rates for these materials are presented at the different laser wavelengths. High quality cutting of the three materials is demonstrated with the 355nm laser and an excimer laser mask projection method is subsequently used to micromachine precision V-grooves as fibre placement structures. Silicon microbenches, used for the integration of multiple-function devices, are also produced using the 355nm laser.
Study of femtosecond laser interaction with wafer-grade silicon
In this paper the interaction of ultra-short pulses (150fs) of laser radiation (wavelength 775nm) over a range of fluences with wafer grade Silicon material in air was analysed using optical and electron microscopy. Optical microscopy was performed by the use of a white light interferometer and a high power optical microscope (magnification 100X). The resolution of both these methods was only sufficient to resolve large dimensions relative to the wavelength of light. For smaller geometries and greater detail, electron microscopy (resolution 1.5nm, 1KV) was used to obtain more information due to its greater resolution and depth of focus. When used in conjunction with surface, cross sectional and transmission imaging, this technique provided the greatest level of detail on the physical processes involved. Using these analysis techniques it was possible to provide a qualitative understanding of the ablation process as a function of laser fluence and to quantitatively describe the depth per pulse over a range of laser fluences, from which a value for the ablation threshold for Silicon (0.17Jcm-2) could be derived.
Production of polymer diffractive optical elements by contact printing
Richard J. Winfield, Martin Meister, Shane O'Brien, et al.
We present the fabrication of phase only diffractive optical elements (DOEs) by contact prints using a novel technique. Phase only DOEs consist of a transparent slide with a surface profile that modulates the phase of an incident laser beam in the desired manner. This surface profile can be exploited to split or to shape the laser beam. In our process a Perspex sheet (PMMA) is exposed through a chrome-on-quartz mask that carries the DOE pattern. The UV light used in the exposure is generated by an ArF excimer laser (l=193nm). The high energy radiation causes photomodification and the phase pattern of the DOE is transferred to the PMMA. While the primary investigations concentrate on binary DOEs, which require one exposure only, we have also attempted to produce multilevel designs which need mask alignment and tighter control of the exposure. At the moment, we study the capability of the method to produce relatively large structures but it might also be possible to use it to manufacture finer structures.
Pulsed laser deposition of wide-bandgap semiconductor thin films
Thin films of ZnO and GaN have been deposited by pulsed laser deposition in atmospheres of oxygen and nitrgoen respectively. A time-of-flight ion probe and optical spectroscopy were used to study the interaction of the ablation plasma with the background gas. The deposition rate was measured using in situ optical reflectivity, and the thin film quality was assessed using x-ray diffraction and photoluminescence. By correlating the plasma measurements and the thin film characterization it was possible to identify the plasma regime required for the deposition of good quality films.
Laser welding of balloon catheters
The balloon catheter is one of the principal instruments of non-invasive vascular surgery. It is used most commonly for angioplasty (and in recent years for delivering stents) at a multitude of different sites in the body from small arteries in the heart to the bilary duct. It is composed of a polymer balloon that is attached to a polymer shaft at two points called the distal and proximal bonds. The diverse utility of balloon catheters means a large range of component sizes and materials are used during production; this leads to a complexity of bonding methods and technology. The proximal and distal bonds have been conventionally made using cyanoacrylate or UV curing glue, however with performance requirements of bond strength, flexibility, profile, and manufacturing costs these bonds are increasingly being made by welding using laser, RF, and Hot Jaw methods. This paper describes laser welding of distal and proximal balloon bonds and details beam delivery, bonding mechanisms, bond shaping, laser types, and wavelength choice.
Poster Session
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Liquid-phase silylation characterization of Shipley SPR500A-series resists using PRIME top-surface imaging process
Khalil I. Arshak, Miroslav Mihov, Arousian Arshak, et al.
Top Surface Imaging (TSI) is a well-established technique used to improve resolution for optical, ultraviolet and electron-beam lithography. The Positive Resist Image by Dry Etching (PRIME) is an advanced lithographic process incorporating electron beam exposure, near UV flood exposure, silylation and dry development. In this paper, the liquid-phase silylation process step in PRIME with Shipley SPR500A-series resists has been experimentally investigated as the most critical part of the process. FT-IR spectroscopy, UV spectroscopy, SIM spectrometry and cross-sectional SEM and TEM were used to characterise the silylation process. Electron-beam exposure with dose in the range of 25-100μC/cm2 at 30KeV was used to crosslinks the resist. Results show that an e-beam dose of 50µC/cm2 was sufficient to prevent silylation in the crosslinked areas. Two bifunctional silylating agents, the cyclic Hexamethylcyclotrisilazane (HMCTS) and the linear Bis[Dimethylamino] dimethylsilane (B[DMA]DMS), were examined and found that they silylate SPR505A much more efficiently than the previously reported Hexamethylcyclotrisiloxane (HMCTSx). The silylation contrast of the PRIME process using HMCTS silylating agent and SPR505A resist was found to be 11:1. The obtained silylated profiles of 1mm lines/spaces gratings for Shipley SPR510A resist have almost vertical sidewalls resulting in very high contrast between the silylated and unsilylated parts of the resist.
Investigation of EUV sources for 13.5-nm operation
Grainne Duffy, Anthony Cummings, Padraig Dunne, et al.
The internationally agreed semiconductor roadmap calls for the development of bright, narrow bandwidth sources of extreme UV radiation for lithography at 13.5 nm. Both pulsed discharge sources and laser produced plasmas have been proposed as possible candidates and xenon is currently the most favored constituent element since it possesses strong emission lines at the correct wavelength. In this paper we show from theoretical considerations that tin containing plasmas provide superior intesitiy, albeit at the expense of increased debris emission. We also show that for laser produced plasma sources, the brightness can be considerably enhanced by varying both the target constituents and the laser pulse profile. Various methods by which the debris problem might be reduced are discussed.
Investigation of a method for the determination of the focused spot size of industrial laser beams based on the drilling of holes in Mylar film
The focussed spot size of industrial laser beams is a critical processing parameter in most laser machining applications as it determines the machined feature size and the irradiance produced by the laser at the material interface. There are a number of standard methods available for accurately measuring and analysing the focussed spot. These methods often require expensive equipment that can be time consuming and difficult to set up in a production environment. This paper presents an investigation into a cost effective and straightforward method for the measurement of focussed laser spot sizes based on drilling of holes in mylar film. It can be shown that the slope of a plot of the square of the hole diameter versus the natural log of the laser pulse energy is equal to twice the square of the spot radius. A measure of the laser spot size can be calculated by generating laser-drilled holes at number of laser pulse energies. The practicality and accuracy of this method is investigated in this paper for a number of laser types including a diode pumped solid state laser (UV DPSS) operating at the third harmonic (355nm), a femtosecond laser and a flash lamp pumped Nd:YAG laser. A comparison between the measured results and the results generated with other available techniques is also presented.
Development and application of an ultrafast laser micromachining workstation
This article describes the development and application of a femtosecond laser micro-machining workstation geared towards the machining of damage free micro-geometries. Much attention has been paid to ultrafast laser micro-machining in recent years given the reported possibilities for machining materials in the absence of thermal damage, and the minimum dimensions that can be machined. The laser systems themselves have evolved from table top lasers to fully packaged commercial systems. The work described in this article details the development of a workstation around a femtosecond laser source to enable controllable micro-machining. A femtosecond laser source with a 1 kHz repetition rate, 800mJ pulse energy, and a pulse width of the order of 150fs was used. A prototype workstation was built around the laser source to incorporate laser monitoring and control, control of laser parameters, high resolution motion, and vacuum technology. Using the system, percussion drilling and surface structuring was performed on stainless steel, aluminium and silicon substrates, and these results are reported.
Vacuum-UV photoabsorption imaging of laser-ablated plumes
John S. Hirsch, Piergiorgio Nicolosi, Luca Poletto, et al.
We describe a new system based on a 1m normal incidence vacuum monochromator with corrected optics that produces a wavelength tunable and collimated vacuum-UV beam. The VUV source is a laser-generated plasma high-Z metal. The primary functin of the system is the measuremtn of time resolved 'images' or spatial distributions of photo-absorption/photoionization in expanding laser plasma plumes. This is achieved by passing the beam through the sample of interest and recording the 'footprint' of the attenuated beam on a CCD. Using the 'photoabsorption imaging' technique we track and extrat column density distriubtions in the expanding plasma plumes. We can also mesaure the plume front velocity. We have characterized the system, particulary in relation to spectral and spatial resolution and the experimental results meet very well expectations from the ray tracing done at the design phase. We present first photoabsorption images of laser produced Ca polumes from the system.
Session 15
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A thermal stack structure for measurement of fluid flow
Hao Zhao, S. J. Neil Mitchell, D. H. Campbell, et al.
A stacked thermal structure for fluid flow sensing has been designed, fabricated, and tested. A double-layer polysilicon process was employed in the fabrication. Flow measurement is based on the transfer of heat from a temperature sensor element to the moving fluid. The undoped or lightly doped polysilicon temperature sensor is located on top of a heavily doped polysilicon heater element. A dielectric layer between the heater and the sensor elements provides both thermal coupling and electrical isolation. In comparison to a hot-wire flow sensor, the heating and sensing functions are separated, allowing the electrical characteristics of each to be optimized. Undoped polysilicon has a large temperature coefficient of resistance (TCR) up to 7 %/K and is thus a preferred material for the sensor. However, heavily doped polysilicon is preferred for the heater due to its lower resistance. The stacked flow sensor structure offers a high thermal sensitivity making it especially suitable for medical applications where the working temperatures are restricted. Flow rates of various fluids can be measured over a wide range. The fabricated flow sensors were used to measure the flow rate of water in the range μl - ml/min and gas (Helium) in the range 10 - 100ml/min.
Carbon dependence of the vibrational mode frequencies in Si1-x-yGexCy alloys
Tatiana S. Perova, Francoise Meyer, Daria Potapova, et al.
A detailed study of the dependence of the vibrational modes in rapid thermal chemical vapour deposited Si1-x-yGexCy on substitutional carbon concentration has been undertaken. The difficulty in incorporating substitutional carbon in these alloys with concentration higher than a few tenths of an atomic percent is well known. It is shown that simultaneous analysis of X-ray diffraction, infrared absorption and Raman scattering measurements can be used to determine the fraction of substitutional carbon from the total carbon content. The frequency shifts of the carbon local modes and the Si-Si modes have been studied in addition to the intensity dependence of the former. The evolution of the carbon satellite peaks and their dependence on total carbon concentration has also been studied. Good numerical agreement with other previously published results has been obtained.
Design of a microfluidic sensor for high-sensitivity copper (II) sensing applications
Ceri Gibson, Patrick Byrne, David Gray, et al.
An all-plastic micro-sensor system for remote measurement of copper (II) ions in the aqueous environment has been developed. The sensing structure was designed for ease of milling and fabricated in poly (methyl methacrylate) (PMMA) using a hot-embossing technique. Issues of sealing the structure were studied extensively and an efficient protocol has been established. The detection system comprises a compact photo-multiplier tube and integrated photon counting system. This method has advantages of low sample volume, (creating a minimal volume of waste), low exposure to contaminants due to the closed system, no moving parts and employs a robust polymer material which is resistant to the environment of intended use. The sensor operates on the principle of flow injection analysis and has been tested using a chemiluminescence (FIA-CL) reaction arising from the complexation of copper with 1,10-phenanthroline and subsequent oxidation by hydrogen peroxide.
Fusion-bonded mutilayered SOI for MEMS applications
David Cole, Cormac McNamara, Kumar Somasundram, et al.
3-stack and 4-stack, 6" dia. multilayered SOI have been fabricated using two different processes, and the bonding ability, thickness uniformity, and stress investigated. High-quality bonding was achieved with good thickness control, independent of the fabrication method used. The stress in the overall structure was controlled by the balance between the combined stress at the oxide silicon interfaces of the SOI buried oxide layers and that exerted by the oxide on the back surface of the handle wafer. An imbalance of 0.5 μm corresponded to a generated bow of about 12 μm. The etch rate of the buried oxide was enhanced along the bonding interface, particularly in the case of an oxide-oxide join, and was found to be strongly dependent on the bond annealing temperature.
Deep reactive ion etching of silicon using an aluminum etching mask
Wei-Chih Wang, Joe Nhut Ho, Per G. Reinhall
A method for fast and efficient deep anisotropic etching of bulk silicon, using a parallel capacitively coupled plasma is presented. The effect of the masking materials and RIE conditions are discussed. Based on the experimental results, a 1000 angstrom thick Al film sufficiently protects the unexposed substrate while allowing the etching of a 350mm deep hole with an area of 3x3mm2 when etching with SF6 /CHF3/O2 plasma. A 2000mm long and 100mm wide (with layers of Al/SiO2/Si and thicknesses of 0.1mm/2.2mm/40mm respectively) cantilever is also achieved. A silicon etch rate up to 2.2 mm/min has be obtained and an anisotropy of A= 0.5 (A=1-V/H, where V=horizontal undercut, H=etch depth) has been observed. The technique was developed mainly for bulk micromachining of silicon or composite silicon cantilever structures.
Session 16
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Optical properties of silver nanowires in nanoporous alumina membranes
Silver nanowires with different diameters are prepared within the pores of nanoporous alumina membranes. The linear optical properties of these composites are investigated (UV-Vis spectroscopy) as well as the nonlinear optical properties (Z-Scan technique). The dependence of both linear and the nonlinear optical properties on the average diameter of the silver wires is analysed, indicating that the spectral position of the plasmon resonance is red-shifted when the wire diameter is increased. This in turn leads to a different nonlinear optical behaviour. At comparatively low incident laser pulse energies all samples show saturable absorption (enhanced transmission). For higher energies, however, a second effect occurs which finally leads to an increase in the absorption coefficient. This second effect can probably be attributed to the ionisation of the silver wires due to multiphoton absorptions and a subsequent trapping of the electrons in the dielectric membrane. The ionised species, however, shows a different optical behaviour. The occurrence of this ionisation depends on the wire diameter. The larger the diameter the lower the incident laser pulse energy needed to ionise the wires. This corresponds to an increase in the linear absorption coefficient with increasing wire diameter.
Third-order nonlinear optical response and nonlinear photoluminescence in multiwalled carbon nanotubes
Margaret E. Brennan, Marek J. Samoc, Takeyuki Kobayasi, et al.
The nonlinear optical properties of multiwalled carbon nanotubes (MWNT) was investigated using femtosecond, picosecond and nanosecond laser pulses by the Z-scan and Degenerate four wave mixing techniques. Measurements show a significant third order nonlinear response in the both visible and near-infrared wavelengths regions, with Χ(3) values as high as 10-10 esu obtained on nanosecond and picosecond excitation and somewhat diminished Χ(3) values of the order of 10-12 esu obtained on femtosecond excitation. The temporal response at both picosecond and femtosecond excitation show a significant fast component indicating that electronic processes contribute to the third order nonlinear optical response of MWNT. This electronic role is highlighted by the observation of Van Hove singularities (VHS) in the density of states of MWNT. Unexpected visible luminescence from MWNT, observed on photo excitation at 1064 nm, is believed to arise from radiative transitions between energy states in the VHS. Our results shows that the presence of VHS enable efficient optical transitions in MWNT and furthermore the enhancement of the third order nonlinear optical response.
Session 17
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Comparative study of two polymer carbon nanotube composites using electron paramagnetic resonance and transmission electron microscopy
We have fabricated two conjugated organic polymer-multiwalled carbon nanotube (MWNT) composites and measured the MWNT content of these two hosts using electron paramagnetic resonance (EPR). These polymers were poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) (PmPV) and poly(9,9-di-n-octylfluorenyl-2,7'-diyl) (PFO). These polymers both disperse MWNTs efficiently but differ in that PFO also suspends graphitic nanoparticles. The fraction of available MWNTs suspended in PmPV rises with increasing polymer mass before saturating at approximately 50% by mass for an optimum soot to polymer mass ratio of 1:4. The optimum settling time for PFO composites was 96 hrs after which 35% of available MWNTs remained suspended. Finally the host polymers were removed by Buchner filtration and the remaining residues were investigated with transmission electron microscopy (TEM). PFO also suspends graphitic nanoparticles with a maximum diameter of approximately 100 nm, which can be attributed to the structure of the polymer itself.
Spectroscopic analysis of the intermolecular interactions of gamma cyclodextrin and carbon nanotubes
Gordon Chambers, Clodagh Carroll, Garrett F. Farrell, et al.
The production of small diameter (0.7-1.2nm) and high purity single walled carbon nanotubes using a gas-phase catalytic approach has aroused considerable interest in the chemistry of this unique material. Most recently it has been proposed that tubes produced in this manner can be cut by simply grinding them in a soft organic material such as g-cyclodextrin. The results reported on such cutting techniques however concentrated upon microscopy thereby limiting the degree of information, which could be deduced about the type of interaction between the two materials. In this study electronic and vibrational spectroscopy as well as Differential Scanning Calorimetry has been performed upon a ground mixture of the aforementioned single walled carbon nanotubes and γ-Cyclodextrin. The mixture was prepared by grinding in a 30:1 ratio γ-cyclodextrin and single walled carbon nanotubes for approximately two hours with the drop-wise addition of ethanol (1ml) in the first 10 minutes. A similar ground mixture of g-Cyclodextrin and multi walled carbon nanotubes was also prepared to help asses the type and degree of interaction between the single walled carbon nanotubes and the γ-Cyclodextrin. Absorption spectroscopy showed changes to the electronic structure of both the single walled carbon nanotubes and the γ-Cyclodextrin, while evidence from Raman spectroscopy indicates that the cyclodextrins are absorbed via van der Waals forces along the length of the tube inducing a compressive strain. No such evidence for an interaction with multi walled carbon nanotubes was observed suggesting the possibility of a diameter selective interaction. Finally as a comparison a sample containing 5mg of tubes was refluxed in an aqueous solution of γ cyclodextrin (0.3M) for ~72 hour similar to early studies preformed on C60 and γ cyclodextrin
Mechanical and thermal properties of carbon-nanotube-reinforced polymer composites
Martin Cadek, Jonathan N. Coleman, Valerie Barron, et al.
In this research study carbon nanotubes were investigated as possible reinforcement agents to improve the mechanical and thermal properties of two different polymer matrix systems. The polymer matrices systems examined were polyvinyl alcohol and poly(9-vinyl cabazole). It was found by adding a range of mass fractions of carbon nanotubes that both Young's modulus and hardness as measured by nano-indentation increased dramatically for both matrices. Thermal properties were examined using differential scanning calorimetry and thermo gravimetric analysis. An increase of 82% in Young's modulus and 63% in hardness was observed for polyvinyl alcohol while adding approximately 1% by weight of multi walled carbon nanotubes. In the case of poly(9-vinyl cabazole) an increase of 200% in Young's modulus and 100% in hardness was achieved, by adding only 8% by weight of nanotubes. As far as the authors are aware this is the highest increase of mechanical properties observed when using carbon nanotube as a reinforcing agent. In addition the thermal properties varied significatly on introduction of the nanotubes. An increase of crystallinity was found for the semi-crystalline matrix, while a second phase appeared for the amorphous polymer when increasing the amount of multiwalled carbon nanotubes. Mechanical and thermal properties of the used polymer matrices could be significantly increased.
Poster Session
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Optical spectroscopy of single-molecule and aggregate hexabenzocoronene derivatives
The low, medium and high concentration luminescence and luminescence-excitation spectra for alkyl substituted hexa-peri-hexabenzocoronene (HBC-C8,2) and hexa(4-n-dodecylphenyl) substituted hexa-peri-hexabenzocoronene (HBC-PhC12) are presented. A study of the concentration dependence of the optical properties of these self-assembling molecular nanowires, in the low to medium concentration regime, associates the spectrum at ~ 10-13 M with the single molecule, and indicates that previously published spectra of HBC's by others were the product of aggregation phenomena. The insertion of an exo-phenyl group between the HBC core and the alkyl side chains, as in HBC-PhC12, was found not to extend the conjugation, but did increase the inhomogeneous broadening of the single molecule luminescence. The continued presence of HBC-PhC12 single molecules, at high concentration, implies that HBC-C8,2 aggregates are thermodynamically more stable than HBC-PhC12 aggregates. In conclusion, the spectroscopic properties of both derivatives were found to be very sensitive to aggregation at low concentration and strongly correlated to the observed macroscopic physical properties.
Single-wall carbon nanotubes as templates for organic molecules
Theresa G. Hedderman, Luke O'Neill, A. Maguire, et al.
Single wall carbon nanotubes are insoluble in most organic solvents such as toluene. Improvements in the solubility of the single wall carbon nanotubes are however seen as a result of specific interactions with molecules such as terphenyl and anthracene. Suspensions formed in toluene with these molecules and the single wall carbon nanotubes are seen to be stable over prolonged periods. Spectroscopic analysis clearly shows an interaction between the carbon nanotubes and the molecules. It is proposed in this study that the use of these more simple molecular systems may help elucidate the nature and extent of the interaction in more complex composite based systems.
In-situ Raman spectroscopy of electrically generated species in fullerene thin films
Siobhan Bridget Phelan, Barry Stephan O'Connell, Garrett F. Farrell, et al.
Organic materials have, in recent decades, been shown to be insulators, semiconductors, or even metallic when doped and the prospect of cheap, easily fabricated devices has attracted much interest. Primitive devices have been demonstrated and yet potentially competitive performance has been limited to polymer light emitting diodes. The recent report that lattice expanded C60 single crystals can be made superconducting, with a transition temperature of 117K, by the injection of charge via a FET type geometry has once again highlighted the potential of C60 in the development of molecular electronic devices. In light of the aforementioned report it is essential that a true understanding of the inter- and intramolecular processes in terms of their contribution to the electronic transport be obtained. In this study the current voltage characteristics of C60 thin film sandwich structures fabricated by vacuum deposition on indium tin oxide (ITO) with an aluminium top electrode are presented and discussed. A strongly non-linear behavior and a sharp increase in the device conductivity was observed at relatively low voltages (~2V), at both room and low temperatures (20K). At room temperature the system is seen to collapse, and in situ Raman measurements indicate a solid state reduction of the fullerene thin film to form a polymeric state. The high conductivity state was seen to be stable at elevated voltages and low temperatures. This state is seen to be reversible with the application of high voltages. At these high voltages the C60 film was seen to sporadically emit white light at randomly localized points analogous to the much documented electroluminescence in single crystals. Moreover the evidence suggests that this highly conducting species maybe similar in nature to a high intensity optically excited species. It is further speculated that the species recently reported in the superconducting lattice expanded C60 single crystals may also be analogous to the highly conducting species observed here.
Analysis of material properties for MEMS using interferometric measurements
Conor O'Mahony, Martin Hill, Alan Mathewson
As the scope and depth of research into microelectromechanical systems increases, the issue of mechanical characterisation has emerged as a major consideration in device design. It is now common to include a set of test structures on a MEMS wafer for extraction of thin film material properties (in particular, residual stress and Young's modulus). These structures usually consist of micromachined beams and strain gauges, and measurement techniques include tensile testing, electromechanical characterisation, SEM imaging, and Raman spectroscopy. However, some of these tests are destructive and difficult to carry out at wafer scale. This work uses electrostatic actuation to pull fixed-fixed beams towards the substrate, and a white-light interferometer to record the beam deflection profile. Finite-element simulation software is employed to model this deflection, and to estimate the material properties which minimise the difference between the measured and simulated profiles. The test is non-destructive, suitable for wafer-level characterisation, and the structures involved require less die space than other methods. We have developed a 1.5mm surface micromachining process for the fabrication of composite and monolayer structures with applications in relay switching, optical imaging and radio-frequency components. This work presents results obtained using interferometric analysis for both monolayer (titanium) and composite (SiOx - metal) thin films fabricated with this process.
Physical interactions between HiPco SWNTs and semiconjugated polymers
Interactions between Arc Discharge single walled carbon nanotubes within polymer composites have been well documented. Here hybrid systems of the conjugated organic polymer poly (p-phenylene vinylene-co-2,5-dioctyloxy -m-phenylene vinylene) (PmPV) and carbon nanotubes produced by Gas-Phase Decomposition of CO (HiPco) process are explored using Raman spectroscopy. Laser excitation wavelengths of 514.5nm and 633nm are employed to determine the specific nature of interaction. Also presented at laser energies 1.96eV and 2.4eV, are hybrid systems of Arc Discharge SWNTs at similar mass fractions to enable a direct comparison of solubility of each nanotube type within the polymer composite to be made. Comparisons are also made between the two hybrid systems in relation to range of nanotube diameters selected at 514.5 and 633nm.
Excited state properties of C60 revisited: a Raman study
Gordon Chambers, Siobhan Bridget Phelan, Garrett F. Farrell, et al.
The excited state properties of C60 thin films have been probed in the temperature range 77-273K using Raman spectroscopy. The change in the Raman pentagonal pinch mode of C60 (whose position is largely independent of temperature) was monitored as a function of the excitation intensity at 514.5nm. This mode, normally positioned at 1469cm-1, was seen to shift reversibly to a lower Raman frequency with increasing laser intensity. Two excited state species have been identified. The first, at 1466cm-1 has been associated with the molecular triplet of C60 as determined from measurements preformed in solution. The second species at 1463cm-1, has been speculated to be an excited state co-operative involving two or more excited states in the solid and is seen to be intrinsic to solid state C60 below the phase transition, as similar measurements in solution show no Raman evolution beyond 1466cm-1. This species observed at 1463cm-1 has previously been reported in the depolymerisation of solid state C60, as well as in reversible processes in C60 crystals and has been characterised by a nonlinear photo-luminescence and photoconductivity. It is further proposed in this study that this excited state is analogous to a number of highly conducting states recently reported for C60. The data presented highlights the existence of a highly non-linear delocalised excited state species at low temperatures which is intrinsic to solid state C60.
Property-structure relationships of some derivatives of poly(m-phenylene vinylene)
Anna Drury, Stefanie Maier, Manuel G. Ruether, et al.
A derivative of poly (m-phenylene vinylene-co-2, 5-dioctyloxy-p-phenylene vinylene) is synthesized using two types of condensation polymerisation reactions, namely Horner-Eammons and Wittig, in three different solvents, toluene, dimethhylformamide (DMF) and chlorobenzene. Although the derivatives formed by each reaction have the same chemical composition it is found that their chemical and optical properties vary. NMR studies show that the morphologies of the polymers are different, due to the differences in cis-trans bond ratio of the vinylene bonds. It is found that the derivatives produced by Horner condensation contain a majority of trans bonds and these derivatives show different spectral characteristics to the Wittig derivatives. The ability of the polymers to disperse carbon nanotubes is also studied. Here, not only is the synthetic route important, but the solvent used also plays a role. The derivatives that are produced by the Horner condensation route in DMF or chlorobenzene are found to have the best binding capabilities with carbon nanotubes.
Nanosecond nonlinear optical extinction in dispersed multiwalled carbon nanotubes excited at 532 nm
Sean M. O'Flaherty, Stephanie V. Hold, Martin Cadek, et al.
Experimental measurements of nonlinear optical extinction of nanosecond laser pulses by a set of conjugated co-polymer/multi walled carbon nanotube composites dispersed in solution is reported here. The polymer poly(meta-phenylenevinylene-co-2,5-dioctyloxy-para-phenylenevinylene) and multi walled carbon nanotube composites were varied according to nanotube mass content. The fabrication technique employed to produce the composite material is discussed. The experiments were performed using an open aperture Z-scan with 6 ns gaussian pulses at 532 nm from a frequency doubled, Q-switched Nd:Yag laser. The nonlinear optical extinction of the incident pulses displays enhanced dissipation of the incident light for lower incident intensities relative to increasing multi walled carbon nanotube content. Either the multi walled carbon nanotubes or the polymer dominates the nonlinear response of the composite depending on the relative mass of polymer to nanotube. Mechanistic implications of the optical dissipation are also discussed and investigated via angular dependent scattering measurements.
Investigation into the structure and quality of carbon/carbon-SiC composites
Tatiana S. Perova, Karl Maile, Abram Lyutovich, et al.
In this work, pyrolytical carbon and C-SixCy-SiC coatings were deposited by chemical vapour deposition (CVD) in a 'Cold Wall' reactor. The C/C samples from 'Schunk Kohlenstofftechnik GmbH', Germany were used as substrates. The pyrolytical carbon coatings were obtained by CH4 cracking at 1200-1300°C. SixCy and SiC coatings were deposited from SiCl4/H2 mixtures by varying the H2/SiCl4 ratio (a). Micro-Raman spectroscopy and X-ray diffraction have been used to determine the order grade for pyrolytical carbon coatings and to investigate the structure and composition of SiC coatings depending on the deposition conditions. In particular, the analysis of Raman spectra of carbon films in the region of 1200-1800 cm-1 allowed the determination of crystal size in a film, which varied from 2.6 to 8.5 nm depending on a. The presence of a strong narrow band at 2712 cm-1 in the second order Raman spectra region (2300- 3400 cm-1) indicated a high degree of perfection of the crystalline lattice and an onion like structure in some of the carbon films. XRD investigation of the SiC-peak showed a shift in frequency and a reduction in intensity when compared to the substrate. The peak shift corresponds to a crystal-geometric grading of the coating.
Covalent attachment of a ruthenium complex to multiwall carbon nanotubes
Sakina Benrezzak, Fiona Frehill, Manuel G. Ruether, et al.
Amino functionalized multi wall carbon nanotubes (MWNT) were reacted with an inorganic Ruthenium complex, {[Ru(dcclbpy)(bpy)2](PF6)2}, in an attempt to covalently attach the Ruthenium complex to the MWNT. The covalent attachment between the Ruthenium complex and the carbon nanotubes is achieved by the formation of an amide group. Absorption and emission spectroscopy indicated that a reaction between the amino functionalized MWNT and the Ruthenium complex occurred. Atomic fore microscopy (AFM) images gave further evidence of a successful attachment of the Ruthenium complex to MWNT by showing multiple junctions between MWNT distinct from naturally occurring splitting of MWNT ropes.
Characterization of nanotube-based artificial muscle materials
Gavin Kiernan, Valerie Barron, David Blond, et al.
Today, many materials are being investigated as possible artificial muscle devices. Nanotubes and conducting polymers are two of the most attractive materials for this application, because of their low operating voltage. In this research, a number of materials are investigated, including nanotube based polymer composites. Methods of characterisation include thermal analysis using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), hot stage microscopy and polarized light microscopy were used to evaluate the morphology of the composites. Fourier transform infrared spectroscopy was used as a compliment to the DSC and hot stage microscopy to examine the crystallinity. Gel permeation chromatography (GPC) was employed to determine the effect of the nanotubes on the molecular weight of the polymer. Since the application of this research is a biomedical device, the biocompatibility of the composites was examined using contact angle analysis and cytotoxicity tests. In summary, results to date indicate that these materials have promise as possible artificial muscle devices.
Gas desorption in single-wall carbon nanotube mats during vacuum annealing
Rory W. Leahy, Krishna Vijayamohanan, Pulickel M. Ajayan, et al.
We report the desorption characteristics of H2O, CO2, H2 and O2, and changes in electrical resistance, single walled carbon nanotube (SWNT) mats during vacuum annealing from room temperature to 873 K. H2O desorption at ~503 K coincides with a resistance decrease of ~ 2%, in agreement with theoretical calculations. CO2 and H2 desorption correspond to subsequent decreases in resistance at ~563, and 663 K respectively. Repeated gas exposures, after thermal desorption, result in reversible R-T characteristics, indicating the tunability of average electrical response of SWNT mats. Our results showing the lack of O2 desorption, and increased CO2 desorption after O2 exposure, show that oxygen is strongly chemisorbed to SWNT surfaces, and desorbs primarily as CO2 and CO. These results are of relevance for harnessing SWNT-based nano-structures for potential applications such as hydrogen storage and chemical sensors, where the resistance-temperature characteristics and gas adsorption phenomena are intimately related.
Spectroscopic characterization of chemically modified porous silicon
Yurii K. Gun'ko, Tatiana S. Perova, S. Balakrishnan, et al.
The discovery of room temperature photoluminescence in porous silicon has opened up a range of applications for this material in new areas such as optical, photodetector, photovoltaic, micromachine and sensors. For this reason there have been significant efforts in recent years directed at modification of silicon surfaces via formation of Si-C and Si-O-E (E = H, C, N) bonds on the silicon surfaces. However, research on bonding of metallorganic fragments to the silicon surface is scant. The main objectives of our work are to develop and investigate new ways of specific chemical bonding of selected metallorganic compounds to the Si surface and to prepare new types of silicon-based materials. New metallorganic composites have been developed on macro- and micro- porous silicon surfaces. The silicon surfaces have been effectively modified using inorganic and organometallic chemistry approaches. The work includes: (i) preparation and investigation of Cl-, HO-, and Cp- modified porous Si-surfaces; (ii) preparation and characterisation of iron oxide layers on porous silicon; (iii) characterization of metallorganic layers on porous silicon by FTIR, EDX and Scanning Electronic Microscopy (SEM). There are strong possibilities that those composite materials will have a wide range of applications in nano-technology and optoelectronics.
Session 19
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Optical sensors for application in intelligent food-packaging technology
Aisling K. McEvoy, Christoph Von Bueltzingsloewen, Colette M. McDonagh, et al.
Modified Atmosphere Packaged (MAP) food employs a protective gas mixture, which normally contains selected amounts of carbon dioxide (CO2) and oxygen (O2), in order to extend the shelf life of food. Conventional MAP analysis of package integrity involves destructive sampling of packages followed by carbon dioxide and oxygen detection. For quality control reasons, as well as to enhance food safety, the concept of optical on-pack sensors for monitoring the gas composition of the MAP package at different stages of the distribution process is very attractive. The objective of this work was to develop printable formulations of oxygen and carbon dioxide sensors for use in food packaging. Oxygen sensing is achieved by detecting the degree of quenching of a fluorescent ruthenium complex entrapped in a sol-gel matrix. In particular, a measurement technique based on the quenching of the fluorescence decay time, phase fluorometric detection, is employed. A scheme for detecting CO2 has been developed which is compatible with the oxygen detection scheme. It is fluorescence-based and uses the pH-sensitive 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) indicator dye encapsulated in an organically modified silica (ORMOSIL) glass matrix. Dual Luminophore Referencing (DLR) has been employed as an internal referencing scheme, which provides many of the advantages of lifetime-based fluorometric methods. Oxygen cross-sensitivity was minimised by encapsulating the reference luminophore in dense sol-gel microspheres. The sensor performance compared well with standard methods for both oxygen and carbon dioxide detection. The results of preliminary on-pack print trials are presented and a preliminary design of an integrated dual gas optical read-out device is discussed.
Fiber Bragg grating sensors: a look-up-table approach to spatial temperature distribution sensing
Alan G. Larkin, John T. Sheridan, Neal O'Gorman
Commercial FBGs (Fiber Bragg Gratings) are used to measure temperature gradients. The measurement system is based on an electronically tuned solidstate laser, S-TLD. Calibration is carried out using a dual Peltier water-cooled system. Spectral parameters are extracted from reflection spectra using LabView software. A 'Look-Up Table' approach is used as a means of solving the inverse scatter problem.
Fluorescence-lifetime-based pH sensing using resorufin
Accurate, non-contact pH sensing is of particular importance in the biological and clinical sciences. Fluorescence lifetime based pH sensing is potentially more useful than intensity based methods because of the reduced sensitivity to excitation source intensity variations, scattering effects, and photobleaching. In this work, we investigate the variation of fluorescence lifetime with pH for resorufin. The intensity averaged lifetime (τ) of resorufin sodium salt in 0.1M phosphate buffer shows an increase of > 3 ns over the 2 -10 pH range, with 90% of the signal change occurring between pH 4 and 8. The fluorescence is not quenched by chloride or oxygen and was unaffected by the ionic strength of the buffer. Resorufin is relatively insoluble in non-alkaline phosphate buffered solutions, but was estimated to increase by ~2 ns between pH 6 and 8. Resorufin and its sodium salt were both incorporated into sol-gels by either acid or base hydrolysis of tetra-methoxysilane (TMOS). Various surfactants were also added to the sol-gels in an attempt to optimise the fluorescence properties and pH sensitivity of the dyes, and to prevent cracking. The sols were then cast from petri-dishes or dip-coated onto acrylic and glass slides. The dyes retained their pH sensitivity, with showing an increase of approximately 2 ns over the pH range 6 - 8. However, leaching of the dye is observed at higher pH and attempt to minimise dye leaching and sol-gel cracking, poly(vinyl alcohol) (PVA) was cross-linked to the silica gel to form a more flexible matrix.
Session 20
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Enhanced polymer waveguide platforms for absorption-based optical chemical sensors
The development of polymer waveguide chips as platforms for optimized absorption-based optical chemical sensors is reported here. The chips were designed in accordance with theoretical predictions published elsewhere relating to the optimization of the sensitivity of optical absorption-based sensors. The waveguides were fabricated by micro-injection moulding and coated with a colourimetric, sol-gel-derived sensing layer. They were then incorporated into a compact, LED-based sensing device for the detection of gaseous NH3. Results presented here demonstrate comparable sensitivity to more complex systems reported to date.
Optimization of the optical detection in a polymer-fabricated microfluidic manifold for the determination of phosphorus
Michaela Bowden, Henning Klank, Oliver Geschke, et al.
Many microfluidic systems have been designed, fabricated and applied to a variety of different analyses in silicon. In recent years attention has turned to polymer fabrication for a number well-documented reasons. The three major advantages of polymer fabrication that have sparked this trend include rapid prototyping, the availability of cheap starting materials and the abundance of polymers with different chemical, physical, electrical and mechanical properties to suit every application. Laser micro machining was chosen for the fabrication of the microfluidic components in this prototype system presented here and polymethyl methacrylate, PMMA as the polymer substrate. The three-layered microfluidic chip was bonded with an applied force at elevated temperatures and leak-free fluidic interconnects were designed. The chosen application for this device is a simple stopped flow measurement in the determination of phosphorus in natural waters. The colorimetric method chosen was based in the formation of the yellow vanadomolybdophosphoric heteropoly acid complex in the presence of inorganic orthophosphate ion in water. Optical detection below 400 nm was achieved with a UV-LED as light source. The optical alignment of the UV-LED through the microfluidic chip at the optical cuvette and the overall integration of the optical components into the manifold were described here.
Temperature-corrected pressure-sensitive paint measurements for aerodynamic applications
Jan Hradil, Claire Davis, Karen Mongey, et al.
Pressure-sensitive paint (PSP) technology is an important new technique, which allows pressure mapping of surfaces under aerodynamic conditions. The principle used is that oxygen in the airflow around the surface quenches luminescence from an oxygen-sensitive dye in the paint and by imaging the illuminated surface with a gated CCD camera, the oxygen profile, and hence the pressure profile of the surface is mapped. The temperature dependence of these paints is a problem. Temperature correction of the surface pressure measurement is often carried out by incorporating a second temperature-sensitive luminophore to provide a surface temperature profile. This usually complicates the measurement process by requiring a second camera or sophisticated filtering to distinguish between the two luminescent processes. In this work, a new oxygen permeable sol-gel coating containing both a temperature (manganese doped magnesium fluorogermanate(MFG) and pressure (Ru(dpp)32+) sensitive luminophore is described. The luminescent lifetimes of each luminophore are separated by several orders of magnitude, allowing pressure and temperature-dependent lifetime measurements to be separated in the time domain. The luminophores were selected such that their absorption bands overlap and their emission spectra occur in adjacent spectral regions thus enabling the use of a single excitation source and single camera. Both lifetimes were measured with a single camera with gated image intensifier. The system thus provides a temperature-corrected surface pressure profile.
Session 21
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Multipath DOAS for tomographic measurements
Potential multi-path spectroscopic differential absorption systems for the measurement of trace gases in the atmosphere are presented. Recommendations are made for system designs to be used for tomographic differential optical absorption spectroscopy (DOAS) measurements. The difficulties in producing multiple simultaneous beams from a single artificial light source are discussed, while the need for further tomographic resolution information is highlighted. An innovative prototype scanning-DOAS system is presented. The system is designed to generate multiple sequential paths, without the need for bulky and expensive mechanical systems. The scanning DOAS system can easily be placed in an industrial production plant or in a street canyon for multiple direction monitoring. The scanning DOAS system is currently being tested at the Cork Institute of Technology (CIT).
Poster Session
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Ratiometric sensor for dissolved oxygen in seawater
Xavier Poteau, Brian D. MacCraith
A dissolved oxygen sensor for marine application is reported which is based on a ratiometric approach to the fluorescence intensity quenching of the ruthenium dye [Ru(II)-tris(4, 7-diphenyl-1, 10-phenanthroline)]2+. Both the ruthenium complex and the coumarin derivative dye have been entrapped in a porous sol-gel film. The membrane shows good optical response on exposure to low levels of dissolved oxygen in seawater. The design and limitations of such an optode membrane are discussed.
Low-level measurements of carbon concentrations in steel using laser-induced plasma spectroscopy (LIPS)
Mohamed A. Khater, John T. Costello, Jean-Paul Mosnier, et al.
Time-integrated, spatially resolved emission spectroscopy, in the deep vacuum ultraviolet (VUV) region (40-160 nm), of laser-produced plasmas has been employed for the quantitative characterization of the carbon content in solid steel target materials; the samples under study contained carbon concentrations in the 0.001-1.32% range. Six prominent VUV carbon spectral lines, representing three different ionization stages, were selected and proved to be spectral-interference free. Several experimental parameters and conditions such as the focusing lens type, laser power density, background atmospheres and pressure were optimized, leading to an unprecedented lower limit of detection, for carbon in solid steel alloys, of 1.2 ppm (parts per million) obtained with the 97.70 nm CIII spectral line. Furthermore, the spectroscopic evaluation of the steel plasma physical parameters is briefly presented.
Immobilization of porphyrins in hydrogels for optical sensing
A. Sheila Holmes-Smith, David Bailly, Mahesh Uttamlal, et al.
This paper describes a new method for the immoblization of metalloporphyrin molecules for optical oxygen sensing. The porphyrin molecules have an acrylamide group attached allowing the porphyrin indicator to be covalently bound within a hydrogel polymer. Two hydrogel monomers: hydroxyethylmethylacrylamide (HEMA) and acrylamide have been investigated to assess their suitability as host polymers for the porphyrins. The photophysics of both the base and Platinum porphyrin: tetra porphyrin are discussed. Platinum tetra porphyrin bound in a hydrogel polymer using HEMA as the monomer unit was found to have a good sensitivity to oxygen.
Development of surface-plasmon-resonance-based immunoassay for cephalexin
Paul P. Dillon, Stephen J. Daly, Johnathan Browne, et al.
The public concern surrounding antibiotic contamination in food and food products has made it imperative to develop analytical methods for their detection. Polyclonal antibodies and protein-hapten conjugates to cephalexin were used in the development of a surface plasmon resonance (SPR)-based inhibition immunoassay to cephalexin. A conjugate consisting of cephalexin-bovine serum albumin (BSA) was immobilised on the dextran gel surface. Dissociation between the antibody and antigen was easily achieved with 10 mmol l-1 NaOH and was very reproducible. Standards of free hapten were prepared and premixed with antibody and, after a suitable incubation time, passed over the surface of the chip with the protein-hapten conjugate immobilised. The hapten in solution inhibited the binding of antibody to the surface resulting in higher response units of antibody bound at lower concentrations of free drug. Model inhibition immunoassays to cephalexin were developed in PBS and spiked milk samples. These assays had detection ranges between 4.88 to 2,500 ng ml-1 and 244 to 3,900 ng ml-1, respectively, with reproducible results.
Development of a portable carbon monoxide optical sensor based on an extended cavity diode laser at 1564 nm
Carbon monoxide (CO) is a major trace gas pollutant with road traffic being responsible for most emissions. Tunable diode laser absorption spectroscopy will be used to measure CO in vehicle emissions, thereby identifying offenders. A portable device will be constructed, which is capable of measuring CO at concentrations of 10 ppm. Design emphasis is on using low cost commercial components. An extended cavity diode laser (ECDL) will be used offering a narrow line width (» 350 kHz) and operated at 1564 nm (near infrared) to allow detection of the CO line R(13). This wavelength has been selected primarily because commercial optics components designed for the telecommunications industry at 1550 nm are readily available and relatively inexpensive. A potential tuning range of 20 nm about the central wavelength for the ECDL also offers potential for detection of other combustion related, gas species in this spectral region using the same diode laser. Novel optical arrangements allowing longer absorption path lengths and hence increased sensitivity of the CO sensor will be investigated. In addition to road traffic pollution measurements, the device will be adapted for use with fibre optic technology, to facilitate air quality measurements in remote locations e.g. stack emissions.
Optical fiber sensor for use in process water systems utilizing FFT-based techniques and artificial neural network pattern recognition
Damien King, William B. Lyons, Colin Flanagan, et al.
An optical fiber sensor is reported which is capable of detecting ethanol in water supplied. A single optical fiber sensor was incorporated into a 1km length of 62.5 μm core diameter polymer-clad silica (PCS) optical fiber. In order to maximize sensitivity, a U bend configuration was used for the sensor where the cladding was removed and the core exposed directly to the fluid udner test. The sensor was interrogated using Optical Time Domain Reflectometry, OTDR as it is intended to extend this work to multiple sensors on a single fiber. In this investigation the sensor as exposed to air, water and alcohol. The signal processing technique has been desigend to optimize the neural network adopted in the existing sensor system. In this investigation the FFT is used and its application leads to an improvement in efficiency of the neural network i.e. minimizing the computing resources. Using SNNS, a feed forward three layer neural network was constructed with the number of input nodes corresponding to the number points required to represent the sensor frequency domain response.
Session 19
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Fluoresence nanotomography: a structural tool in biomedical sensing
Fluorescence nanotomography (FN) is a newly developed method for determining molecular distributions on a nanometre scale in soft solids, biological macromolecules and medically important systems. FN uses fluorescence resonance energy transfer (FRET) for the recognition of the separations between molecules. By using a fluorescence lifetime measurement of sub-nanosecond time resolution, the spatial resolution of the resulting distribution function can be better than 1 Å. In this paper the theoretical background of the method is outlined and the results of simulations on model molecular distributions presented. This is followed by demonstration of several applications of FN to real molecular systems, including bulk solutions of molecules of different sizes, complexes, porous polymers, phospholipids and sugar-protein competitive binding sensors glucose. The experimental requirements of FN as a structural tool for wide class of biomedical systems are discussed.
Poster Session
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Using fluoresence spectra to distinguish between microalgae species
Spectral characteristics based on in-vivo fluorescence measurements were taken of five laboratory uni-algal cultures: Isochrysis galbana, Nannochloris atomus, Tetraselmis chui, Tetraselmis pseuicia and Tetraselmis seucica. Two diffrent techniques for fluorescence measurements have been used to detection of fluorescence of marine algae. The techniqeus used were Confocal Microscope LSM 510 and LabRam 1B Spectroscopic Microscope. Both instruments were able to detect the in vivo fluroescence signal of all uni-algal cultures. Different excitation wavelengths have been used. The excitation wavelength of 488 nm produced the fluorescence signal with highest intensity. Confocal fluorescence microscopy shows that the samples are spectrally uniform from cell to cell. This result suggests that fluorescence measurements can be used for identification of algal species. Raman spectroscopy is employed to identify differences in molecular structure between the samples. Chlorophyll fluorescence of different species shows a change. As fluorescence is directly linked to the physiological state of the photosynthetic system and very sensitive to stress being experienced further research in the direction of fluorescence detection of toxic algae species will be of interest.
Environmental sensing of hydrocarbons in water using mid-infrared optical fibers
Raymond P. McCue, James Edward Walsh, Fiona Walsh, et al.
The sensing of hydrocarbons, such as the BTEX compounds in water, is described. These hydrocarbons, which are constituents of petroleum can find their way into groundwater due to leaks in underground tanks and in associated piping, are known to be carcinogenic and threaten flora and fauna. An infrared fiber optic sensor based on the evanescent wave generated around the bare core fiber is utilised to perform qualitative and quantitative measurements on these analytes. A silver halide fiber is used for its low spectral attenuation between 4-16mm, for within this wavelength range the analytes have characteristic absorption peaks, which allow their concentrations in water to be determined using the Beer Lambert Law. Using narrow bandpass filters centred on a characteristic peak, the sensor can be selectively tuned to a single analyte. Coating the bare core with a hydrophobic plasticised PVC film increases analyte concentration within the active region of the sensor and minimizes water interference, which is considerable at these wavelengths.
Computed tomography of air pollutants in street canyons
We present the results of preliminary research investigating the generation of two-dimensional pollutant gas concentration maps of street canyons. This research uses computed tomography (CT) to reconstruct the spatial distribution of gas concentrations from path-integral data obtained using differential optical absorption spectroscopy (DOAS). This work represents a novel application of these two techniques and is aimed at the validation of theoretical gas distribution models in selected urban settings. The derived results are based on model data and investigate the viability of constrained geometry sensing networks and the accuracy of current computed tomography algorithms. We also present results on the use of an evolutionary algorithm applied to pollutant reconstruction in an open area as part of initial investigations into its applicability to street canyon pollutant reconstruction. Future work will include the reconstruction of gas distributions in a real urban setting with the long-term goal of a system that is capable of performing this task in near real-time allowing the visualisation of short to medium time scale spatial dynamics.
Session 23
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Raman fiber preamplifier for 200-km 10-Gbit/s DWDM optical link.
Art T. O'Hare, J.-L. Barbey, Nicholas Brochier
Measurements are presented of Raman coefficients of two types of commonly installed fobre. In addition, a Raman pre-amplified single span DWDM link on NZDSF fiber is presented which allows for increased transmission distances of up to 200 km.
Application of spectral reflectivity to the measurement of thin-film thickness
The aim of this work is to investigate the application of the spectral reflectance technique to thickness measurement of highly localised semi-transparent coatings on miniature geometries, such as those used in the medical devices industry. The paper will describe the application of the technique to coatings on curved or non-uniform surfaces such as narrow-bore metal tubes and thin wires. The paper will describe the equipment used including a spectrometer with micro-focus attachment, and optical modelling software. This work also involved laser-drilling of the polymer films to allow complementary step-height measurements to be made. Special steps were also required to overcome problems in measurement due to the transparency of the thin films. Complementary techniques including white-light interferometry, which were used to benchmark the method, will also be described.
Applications in holographic and electronic speckle pattern interferometry of a photopolymer holographic recording material
This paper presents the use of an acrylamide-based photopolymer as the recording medium in holographic Interferometry. The recorded hologram can also provide a speckle reference image for out-of-plane sensitive electronic speckle pattern interferometry. This dual use of the hologram is demonstrated in the testing of thick plastic PVC pipes, which were internally pressurized. The radial strain was measured using holographic interferometry by measuring the out-of-plane motion of the object due to a known change in pressure inside the cylinder. The radial strain for the same magnitude of internal pressure change was also investigated using electronic speckle pattern interferometry (ESPI) by using the hologram stored in the photopolymer acting as a holographic optical element. A hologram was also recorded at a wavelength of 532nm and the image was reconstructed at laser diode wavelength of 784nm. The hologram was used in an ESPI system as before. As the diode can be wavelength modulated, digital phase shifting can be implemented in both interferometric techniques for detailed fringe analysis.
Mechanical characterization of polyvinylchloride pipes using electronic speckle pattern interferometry
The use of electronic speckle pattern interferometry (ESPI) for non-destructive material characterization of thick and thin unplasticized polyvinylchloride (uPVC) pipes is presented. Pipes are tested by internal pressurization and ESPI gives a complete mapping of the resulting displacement field over the area imaged by the video camera. The results for the strain derived from ESPI data and from the standard mechanical method using strain gauges agree very well with each other. The interferometric method used is non-contact and gives high-confidence results for Young's modulus of uPVC pipes. The fringe counting method gives the total diplsacment over the field of view imaged by the CCD camera and is subject to a fringe error of 0.5. This simple approach is valid when the displacement behavior of the sample is known. When this is not the case then it is necessary to calculate the phase map of the displacement of digitally shifting the phase difference between the two beams in the interferometer. We have implemented this technique by modulating the laser diode drive current to alter the wavelength of the laser very slightly between frames. A linear phase map of the displacement is always obtained in the present case.
Poster Session
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Evaluation of high-frequency vibrations using electronic speckle pattern interferometry
Vincent Toal, Henry Rice, Craig Meskell, et al.
The available techniques for the study of high frequency vibration using electronic speckle pattern interferometry (ESPI) are briefly surveyed. We concentrate on two methods in particular. The first is a straightforward approach in which a CCD camera is used having a frame rate of at least twice the highest vibration frequency so that the sampling criterion is satisfied. The images are processed and analysed off-line. Digital phase shifting can be also implemented for detailed fringe analysis. The second approach is time-averaged ESPI in which the Bessel fringe function can be analysed in real time by modulating the optical path difference in the interferometer. This can be done either by using a vibrating component or, as in the present work, by direct modulation of the laser wavelength at the frequency of the vibrating mode.
Ultraviolet spectrophotometry of contact lens materials
Ultraviolet radiation is potentially damaging to ocular tissues. Incorporation of UV-blocking monomers into contact lens materials provides attenuation of this radiation, leading to a reduction in UV incidence at the corneal surface. The extent and spectral characteristics of this attenuation varies according to lens type and parameters. Spectrometry has traditionally been used to measure UV attenuation of a contact lens. A novel contact lens holder was designed and constructed to facilitate the mounting of the lens in an intact and hydrated state during measurement. The UV transmission characteristics of two commercially available hydrogel contact lenses were investigated using the Perkin Elmer Lambda900 UV/VIS/NIR dual beam spectrometer.
Session 24
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Analysis techniques for investigation of photoresist silylation processes
Thomas J. Kinsella, Arousian Arshak, Declan McDonagh, et al.
In this work, the authors explore the application of tetramethylammonium hydroxide (TMAH) developer chemical as a staining agent to enhance the top-down contrast of a silylated pattern to optical detection. When examining a silylated latent image top-down, the topographical differences generated due to the swelling of the silylated region are relied upon to identify pattern details. However, for lower exposure energy or shorter silylation times, there may not be sufficient silicon incorporation to allow clear identification of specific structures for cleaving. The authors have used the TMAH staining technique proposed by La Tulipe et al. to enhance the relief top-down, thereby facilitating analysis of even mildly silylated samples. Results will be presented illustrating the contrast enhancement after staining. Cross-sections of film profiles after aqueous silylation of an I-line photoresist with a solution of hexamethylcyclotrisilazane will also be generated.
Session 25
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Nonlocal material response of photopolymer holographic materials
The non-local model assumes that monomer molecules are polymerised to form polymer chains and that these chains are not constrained to the illuminated regions, i.e. they are non-local. A non-local response function was added to account for this non-local effect. In this paper the generalised model previously published by the authors was further extended to allow for non-linear proportionality to the recording illumination. The resulting equations are presented in this paper. The two harmonic analytic formulae for this extended generalised response function model are also presented in this paper.
A modular camera system for high time-resolution photometry
Daniel J. Buckton, Oliver Ryan, Andrew Shearer, et al.
A new modular high time resolution imaging camera system with sub-microsecond timing accuracy has been built in the Physics Dept. of NUI, Galway. The system was designed to be mounted on large telescopes for observing the temporal, spectral and polarisation characteristics of faint astronomical objects, such as optical pulsars. The camera system developed allows simultaneous and independent observing of multiple wavebands of emission from the target objects. This is achieved using optics that split images into their different spectral or polarisation components. The system currently incorporates a multi-anode microchannel array (MAMA) photon detecting and imaging camera with a time resolution of up to 100ns. This is combined with three high quantum efficiency avalanche photodiodes (APDs) with count rates of up to 16 million photons per second. The high time resolution recording system can allow for the removal of telescope tracking inaccuracy and wind shear off-line. This yields better PSFs for bright objects such as crowded globular star clusters. This combination of different detectors allows the system to be operated as a multi purpose, high QE, high time resolution system. The modular nature of the design electronics also allows the addition and removal of detectors without limiting the performance of other elements within the system. The data path is also designed so that archiving integrity is maintained while the data path is simultaneously used for real-time analysis and display systems. Future applications in the bio-medical imaging sector are envisaged for high time resolution fluorescence imaging, and astronomical polarisation studies.
Design of phase-only DOEs with a high signal-to-noise ratio
Martin Meister, Richard J. Winfield
We report on the design of phase only diffractive optical elements (DOEs) with a locally improved signal to noise ratio. The formation of low noise regions is particularly useful for designs where it is difficult to achieve low background noise throughout the entire reconstruction. Such a case may arise in highly quantized elements or elements with a small spatial bandwidth. The DOE design is achieved by a direct search algorithm which allows for the definition of arbitrary low-noise areas in the reconstruction plane. However, the method is not restricted to direct search and should work with all direct schemes. While the local suppression of noise works rather well other performance criteria like diffraction efficiency and reconstruction error do, in practice, not suffer much from the additional constraints. This is due to the advantage that amplitude freedom and phase freedom can be maintained in large areas of the reconstruction. It is shown how this approach may be used in the design of beam splitters to prevent the formation of unwanted repeated spot patterns.
Poster Session
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Lasing properties of semiconductor microcavity lasers
Microcavity semiconductor lasers are important devices from both practical and fundamental viewpoints. Practically, these lasers/resonators are excellent candidates for the next generation of all-optical network components, including switches and filters, because of their size and low power consumption. We will present a novel packaging scheme which further facilitates these applications. This scheme involves the bonding of the optically pumped micro-resonator to a piece of multi-mode fiber. The laser is optically pumped directly and the emission is collected through another multi-mode fiber. This raises the possibility for 'all fiber' packaging schemes where the micro-resonator is sandwiched between two pieces of optical fiber. The pump and signal light can be injected in at one end and the output collected at the other. This illustrates the potential that these devices have for all optical network applications. In addition, the dynamic properties of these lasers are not well understood because the low level of laser light (order of nanoWatts) makes experimental analysis difficult. We will present experimental results that highlight some of the future challenge, which will have to be overcome if these devices are to realise their potential.
Measurement system for photodetector characterization
Anssi Jaakko Maekynen, Sampo Backman, Juha Tapio Kostamovaara
A measurement system for electro-optical characterization of photodetectors and photodetector arrays is presented. The system is intended for laboratory use where typically a few devices are characterized at a time. The instrument is designed for determining the photoresponse (dc and pulse) of a single photodetector or a photodetector array as a function of wavelength, position, and temperature. In case of photodetector arrays, the measurement of modulation transfer function (MTF) and fast determination of its photoresponse nonuniformity (PRNU) is also possible. The instrument setup and experimental results are presented.
Session 24
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Overview of sports vision
Linda A. Moore, Jannie T. Ferreira
Sports vision encompasses the visual assessment and provision of sports-specific visual performance enhancement and ocular protection for athletes of all ages, genders and levels of participation. In recent years, sports vision has been identified as one of the key performance indicators in sport. It is built on four main cornerstones: corrective eyewear, protective eyewear, visual skills enhancement and performance enhancement. Although clinically well established in the US, it is still a relatively new area of optometric specialisation elsewhere in the world and is gaining increasing popularity with eyecare practitioners and researchers. This research is often multi-disciplinary and involves input from a variety of subject disciplines, mainly those of optometry, medicine, physiology, psychology, physics, chemistry, computer science and engineering. Collaborative research projects are currently underway between staff of the Schools of Physics and Computing (DIT) and the Academy of Sports Vision (RAU).
Poster Session
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Quasi-optical analysis of the HIFI instrument for the Herschel Space Observatory
In this paper we detail the optical design of HIFI, one of three instruments to be flown on the Herschel Space Observatory and also outline the general approach taken in analysing the quasi-optical performance of the instrument. Gaussian Beam Mode Analysis theory is the principle technique chosen for the quasi-optical analysis, supplemented by the commercially available optical analysis package GLAD. These quasi-optical techniques are used for validation of the optical design and predicting the performance of the HIFI system. The HIFI system was checked for issues such as truncation, mechanical misalignment and aberrational losses, along with aperture efficiency and LO coupling efficiency. The quasi-optical analytical methods described could be applied generally to long wavelength optical instruments.
Fast lens testing using random targets
Sampo Backman, Anssi Jaakko Maekynen, Timo T. Kolehmainen, et al.
The performance of a random target method for fast MTF measurement of a lens is evaluated. Although the method is well-known, its potential for fast lens testing has not been assessed in the open literature. To optimize speed, the simplest possible instrument setup with minimum amount of mechanical movements during measurement execution is used. The setup includes only a random target, lens under test and a CCD camera with focus adjustment. The target consists of a random black and white pattern of a flat spectrum. The MTF of the lens is acquired by imaging the random target on the CCD using the lens, and then analyzing the spatial frequency content of the image using an ordinary PC. It was found out that a suitable compromise between speed and precision is achieved using a matrix of 128*128 samples per measured field point. This provides better than 2% precision and a few second's total execution time per lens including best focus evaluation and the measurement of tangential and sagittal MTF curves of 5 field points. Using commercially available components, measurement frequencies up to 100 cycles/mm seem achievable using the simple instrument setup.
Direct integration diffraction-based analysis and synthesis algorithms for laser optical systems
An algorithm for diffraction-based modeling of optical systems for laser devices has been developed. The direct integration is used for the Rayleigh-Sommerfeld formula throughout the system, so optical elements with non-plane surfaces may be adequately treated. The integration is based on the modified Cotes quadrature formula and ensures both high accuracy and speed. A method for the diffraction-based search for an initial scheme for optimization is also proposed. Thus the whole synthesis procedure for a laser optical system may be performed on the basis of diffraction theory.
Session 27
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Near-infrared surface-enhanced-Raman-scattering (SERS) mediated identification of single optically trapped, bacterial spores
A novel methodology has been developed for the investigation of bacterial spores. Specifically, this method has been used to probe the spore coat composition of several Bacillus species. This technique may be useful in many applications; most notably, development of novel detection schemes toward potentially harmful biological agents. This method would also be useful as an ancillary environmental monitoring system where sterility is of importance (i.e., food preparation areas as well as invasive and minimally invasive medical applications). This unique detection scheme is based on the near-infrared (NIR) Surface-Enhanced-Raman-Scattering (SERS) from single, optically trapped, bacterial spores. The SERS spectra of several bacterial spores in aqueous media have been measured using SERS substrates based on 60-nm diameter gold colloids bound to 3-Aminopropyltriethoxysilane derivatized glass. The light from a 785-nm laser diode was used to capture/manipulate as well as simultaneously excite the SERS of an individual bacterial spore. The collected SERS spectra were examined for uniqueness and the applicability of this technique for the species identification of bacterial spores.
Machine learning methods for quantitative analysis of Raman spectroscopy data
The automated identification and quantification of illicit materials using Raman spectroscopy is of significant importance for law enforcement agencies. This paper explores the use of Machine Learning (ML) methods in comparison with standard statistical regression techniques for developing automated identification methods. In this work, the ML task is broken into two sub-tasks, data reduction and prediction. In well-conditioned data, the number of samples should be much larger than the number of attributes per sample, to limit the degrees of freedom in predictive models. In this spectroscopy data, the opposite is normally true. Predictive models based on such data have a high number of degrees of freedom, which increases the risk of models over-fitting to the sample data and having poor predictive power. In the work described here, an approach to data reduction based on Genetic Algorithms is described. For the prediction sub-task, the objective is to estimate the concentration of a component in a mixture, based on its Raman spectrum and the known concentrations of previously seen mixtures. Here, Neural Networks and k-Nearest Neighbours are used for prediction. Preliminary results are presented for the problem of estimating the concentration of cocaine in solid mixtures, and compared with previously published results in which statistical analysis of the same dataset was performed. Finally, this paper demonstrates how more accurate results may be achieved by using an ensemble of prediction techniques.
Spectroscopic study of food and food toxins
Fungal infection of food causes billions of dollars of lost revenue per annum as well as health problems, to animals and humans, if consumed in sufficient quantities. Modern food sorting techniques rely on colour or other physical characteristics to filter diseased or otherwise unsuitable foodstuffs from healthy foodstuffs. Their speeds are such that up to 40,000 objects per second can be moved at 4 metres per second, through 1 m wide chutes that offer a wide view for colour and shape sorting. Grain type foods such as coffee or peanuts are often vulnerable to toxic infection from invading fungi. If this happens, then their texture, taste and colour can change. Up to now, only visible wavelengths and colour identification have been used to bulk-sort food, but there has been little research in the ultra violet regions of the spectrum to help identify fungus or toxin infection. This research specifically concentrated on the ultra violet (UV) spectral characteristics of food in an attempt to identify possible spectral changes that occur when healthy food items like peanuts become infected with toxin-producing fungi. Ultimately, the goal is to design, build and construct an optical detection system that can use these 'spectral fingerprints' to more quickly and efficiently detect toxically infected food items.
Stokes/anti-Stokes Raman spectroscopy of HiPco single-walled carbon nanotubes
An analysis of the Raman spectra of single-walled HiPco carbon nanotube powder using laser energies of 1.92 eV, 2.4 eV, 2.5 eV, and 2.7 eV, including a comparison of the Stokes and anti-Stokes contributions is presented. The diameter distribution was determined to be 0.8-1.2nm from the spectral positioning of the Radial Breathing Modes. The diameter distribution is consistent with that determined by NIR absorption spectroscopy. At all excitation energies the profile of the G-line indicates a predominance of semiconducting tubes although at 2.4 eV there is some indication of some contribution from metallic tubes. In all cases the anti Stokes line was weak and the Stokes/anti Stokes ratio was at least an order of magnitude indicating at most weak resonance enhancement in either.
Local field effect on infrared phonon frequencies of thin dielectric films
Igor I. Shaganov, Tatiana S. Perova, Alan Moore
A number of thin dielectric films deposited onto aluminated glass substrates and onto the materials transparent in the IR range (silicon, KRS-5 and CsI) were investigated using infrared transmission and reflection-absorption techniques. The application of these techniques to thin dielectric films at normal and oblique incidence of light allows the observation of both the longitudinal and transverse optical phonons. The longitudinal (LO)-transverse (TO) optical phonons splitting is analysed in terms of a dispersive local field effect. It has been shown that the results of LO-TO splitting obtained from dispersive local field effect are in a good agreement with the results obtained from the dynamical theory of crystalline lattices.
Intermolecular interactions in molecular systems: pros and cons
For applications as diverse as molecular electronics and nonlinear optics, organic molecular systems have long been vaunted as ideal candidates due to their low cost and the tailorability of their physical properties through well explored organic chemistry. Indeed, examples of porphyrins and systematically structured oligomers show how the properties of these systems can be finely tuned leading to simple structure-property relationships. In most cases, however, these finely tuned properties are lost in the solid state, and even at moderate concentrations in solution, as illustrated for the liquid crystal forming materials, hexabenzocoronenes. Not only are structure property relationships lost, but the optical properties, in particular fluorescence efficiency, are greatly suppressed. In polymers, which are structurally less defined, such aggregration effects can be both interchain and intrachain and have been seen to depend on the backbone isomerism. Raman spectroscopy has been shown to be a valuable probe of the purity of the backbone isomerisation and thus of the inhibition of interchain interaction. The use of nanospacers has been also explored for the local inhibition of intermolecular interaction. In particular, carbon nanotubes are shown to selectively interact with organic polymers in order to reduce the polymer-polymer interaction and so enhance fluorescence in the solid state. Minimisation of the interaction between molecules in order to preserve the as designed properties is a further challenge to molecular science. In fullerenes in the solid state, however, it appears that interaction between excited state species enhances both the electronic and optical properties of the material. The insulating, weakly optically active crystalline material becomes highly fluorescent and highly conducting under high intensity illumination. The origin of the nonlinear process is proposed to be an optically induced insulator to metal transition as a result of the increased interaction of neighbouring excited states. It is proposed that while in many molecular systems intermolecular can be detrimental, they do potentially offer a further design parameter to the molecular scientist.
Session 28
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Influence of chemical composition on the fluorescence lifetimes of crude petroleum oils
Fluorescence based methods are increasingly being used for the analysis of crude oils because they offer high speed, low cost, non-contact, and non-destructive testing options. The fluorescence of crude oils is due to the presence of a wide range of cyclic aromatic compounds, the intensity and temporal behaviour of this fluorescence is directly related to chemical composition. In particular, we have found that the Fluorescence Lifetime (FL) measured at a range of different emission wavelengths is correlated with the concentrations of the aromatic and polar fractions of petroleum oils, and the density (API gravity). We have analysed 22 different crude oils from around the world with API gravities of between 10 to 50. The fluorescence steady-state emission spectra and fluorescence lifetimes at a range of emission wavelengths were measured for 380 nm excitation. It was found that the correlations between the chemical and physical characteristics of the crude oils and the measured fluorescence parameters are highly non-linear. Furthermore, there is a wide degree of scatter in the observed data for medium oils, which have similar physical properties but widely varying chemical compositions. We discuss these findings in the context of developing quantitative methods of analysis for crude petroleum oils based on fluorescence lifetime measurements.
VUV and soft x-ray emission from pre-plasmas irradiated with picosecond and femtosecond pulses
Adrian Murphy, John S. Hirsch, Deirdre Kilbane, et al.
We report here some observations and preliminary findings from a study focussed on the vacuum-UV (λ, 40-60 nm) radiation emitted during the interaction of 150 ps laser pulses (100-400 mJ) with copper pre-plasmas formed by an electro-optically synchronised (0.1 - 0.8 J, 8 ns) long pulse laser. We have observed significant gains in VUV flux that scale with inter-laser delay. We also report preliminary observations on total X-ray emission from the interaction of a superintense 80 fs, 200 mJ laser pulse at the UK ASTRA laser facility with a similar pre-plasma at irradiances approaching 1019 W/cm2
Session 29
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Development of infrared water sensors based on novel light sources
John R. Donohue, Hugh Joseph Masterson, Gwenael Maze, et al.
The detection and measurement of vapour-phase or liquid-phase water is important in many industrial and chemical processes. Water exhibits strong absorption bands compared to other substances in the near infrared (NIR), and for this reason NIR spectroscopy is especially well suited to moisture determination. A lack of suitable sources in the NIR, however, has impeded the application of optical sensors to water detection. We have developed a modulatable IR source for use in a moisture sensor. In the system, the luminescent emission from optically pumped rare earth doped glasses is used. Thulium doped zirconium fluoride glass, which luminesces at 1.83 mm was the material chosen. The spectral overlap with the water absorption band is significant, and the output stability matches that of the pump source, which is typically an internally modulated diode laser emitting at 685nm. The detection system uses a reference beam and a probe beam to monitor changes in absorption due to moisture or water vapour. Results illustrating the effectiveness of the novel IR source in a sensor platform to measure trace amounts of liquid water and water vapor will be presented.
Optical cure monitoring for process and quality control in DVD manufacture
Patrick Byrne, Kieran O'Dwyer, Brian D. MacCraith, et al.
An optical sensor system, which provides real-time process information during the curing of DVD adhesive within the DVD manufacturing process, is reported. Incomplete or non-uniform curing of the adhesive in the centre of the disk can cause variation in layer thickness or create stresses, which may cause warping of the disk. The monitoring of adhesive cure is then of vital importance to manufacturers, particularly if this can be achieved in situ and within the production cycle time for disk manufacture. The operating principle of the sensor is the detection of changes in the infrared absorption spectrum of the adhesive as it cures. The use of infrared absorption in itself is not straightforward as the adhesive is sandwiched between two polycarbonate disks. One of these disks is completely opaque throughout the infrared due to the aluminium layer deposited on it and the other disk has a semi-reflective layer of a material such as silicon, gold or silver. The sensor employs a reflectance based interrogation technique, which uses the highly reflective aluminium coated surface of the DVD. The work described here deals principally with (i) definition of the specifications of the sensor system and the measurement methodology, (ii) development and optimization of a laboratory prototype sensor and (iii) design of an industrial prototype system. Results are presented from both prototype systems.
Improvement of UV on/off ratios of a gated ICCD by simultaneously gating the MCP
Stephen Hamilton, Emer Conroy
Gated image intensifiers (Gen II) have been quoted in the past of having On/Off, or rejection ratios, of 107. In this paper we investigate the relationship of the On/Off ratio with incident wavelength. The data shows that the On/Off ratio can vary by as much as 102 with values of only 104 at ~200nm for a given image intensifier. This low On/Off ratio can limit the sensitivity of an Intensified CCD camera under certain conditions where there is an abundance of UV, such as spectral imaging in combustion research. This is particularly true in situations where the CCD exposure and readout times, typically milliseconds, take much longer than the required 'On' time of the photocathode, which is typically nanoseconds. Test data also shows the advantage of switching the MCP On and Off simultaneously with the photocathode, which brings the rejection ratios up to >108.
Miniaturized differential optical absorption spectroscopy (DOAS) system for the analysis of NO2
J. Alberto Morales, James Edward Walsh, Jack E. Treacy, et al.
Current trends in optical design engineering are leading to the development of new systems which can analyze atmospheric pollutants in a fast and easy way, allowing remote-sensing and miniaturization at a low cost. A small portable fiber-optic based system is presented for the spectroscopic analysis of a common gas pollutant, NO2. The novel optical set-up described consists of a small telescope that collects ultraviolet-visible light from a xenon lamp located 600 m away. The light is coupled into a portable diode array spectrometer through a fiber-optic cable and the system is controlled by a lap-top computer where the spectra are recorded. Using the spectrum of the lamp as a reference, the absorption spectrum of the open path between the lamp and the telescope is calculated. Known absorption features in the NO2 spectrum are used to calculate the concentration of the pollutant using the principles of Differential Optical Absorption Spectroscopy (DOAS). Calibration is carried by using sample gas bags of known concentration of the pollutant. The results obtained demonstrate that it is possible to detect and determine NO2 concentrations directly from the atmosphere at typical environment levels by using an inexpensive field based fiber-optic spectrometer system.
Poster Session
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Optical characterization of high-k dielectrics HfO2 thin films obtained by MOCVD
Mircea Modreanu, P. K. Hurley, B. J. O'Sullivan, et al.
The optical properties of a set of high-k dielectrics HfO2 thin films obtained by two different modified metal organic chemical vapour deposition (MOCVD) techniques were studied using spectroscopic ellipsometry (SE). HfO2 thin films with thickness varying from 10-40 nm were formed over a range of temperatures (300-425°C). After deposition the sample were annealed by Rapid Thermal Annealing (RTP) at 800°C in an oxygen/argon ambient and UV annealing at 400°C in oxygen. The films were analysed physically using XRD and FTIR. The XRD results show that as-deposited HfO2 films microstructure strongly depends on deposition temperature. Both polycrystalline (T>365°C) and amorphous films (T<320oC) were formed. The polycrystalline structure is identified as monoclinic. The SE results demonstrate that as-deposited amorphous HfO2 thin films have a high degree of porosity. After annealing at 800oC in oxygen and in nitrogen ambient, due to the solid phase crystallisation, as-deposited amorphous HfO2 thin films become crystalline and the film porosities are strongly reduced. In addition, an increase of the refractive index and a decrease of the film thickness are also obtained. Optical properties of the as-deposited polycrystalline HfO2 are also improved after annealing and an increase of the refractive index and a decrease of the film thickness is also obtained.
Study of structure and quality of different silicon oxides using FTIR and Raman microscopy
Cormac Moore, Tatiana S. Perova, Barry J. Kennedy, et al.
In this work, SiO2 and fluorine and phosphorous doped SiO2 thin films are investigated using FTIR and Raman techniques. FTIR spectroscopy was performed at normal and oblique incidence of the probe beam in transmission and reflection modes. The effect of polarisation and angle of incidence of the probe beam is examined for the case of reflection mode. Infrared spectra taken from doped oxides show that the structure changes with the passage of time. Alternate methods to calculate the thickness of the doped film are therefore discussed. Infrared spectra of electron beam evaporated oxides give valuable information on their structure and water content. The porosity is calculated for these samples. Finally, micro-Raman spectroscopy is used to measure the fluorine content in a device structure.
Nonlinear optical properties of metal and semiconductor nanoparticles
Aine M. Whelan, Sakina Benrezzak, Margaret E. Brennan, et al.
The synthesis of metal (Au,Ag) and semiconductor (PbS) nanoparticles of specific morphology and shape is reported. The shape of PbS nanoparticles has been varied from spherical to oval to cubic, by use of poly(vinyl alcohol) (PVA), DNA and ethylene glycol as stabilisers respectively. For the first time, a seeding method has been used to successfully prepare PVA stabilised gold and silver nanoparticles. Characterisation of the third order optical nonlinearity of the nanoparticles has been carried out using the Z-scan technique with values of Im ÷ (3) as large as 10-10. Modulation of the magnitude of the nonlinear optical response with morphology in the case of the PbS nanoparticles is presented.
Wide-field fast scanning spectrograph
A scanning spectrograph was designed and constructed to provide a new capability for measuring spectra of spatial and temporal recurring atmospheric luminous phenomena. This phenomena may be a new form of natural energy, which exists on several areas of the Earth. Because of the phenomena is often a moving target, existing spectographs are unable to record a spectrum. The instrument is best suited for measuring extended emission line sources, but it is also suitable for work on bright stellar objects, moving sources such as meteors and comets, and conventional indoor industrial applications where a wide field of view and/or a moving target is involved. The challenge of tracking the target is carried out by all-sky cameras. They are used to obtain the target coordinates, which triggers the tracking spectrograph through a multiplexer. The scanning spectrograph uses a high-speed lens system. It projects the incoming wide field light through a horizontal moving slit assembly onto a reflective grating based on a rotary platform that is synchronized with the slit mechanism. The slit width is adjustable, as is the case in conventional spectrographs. An important part of the design is the lateral movement of the entire slit assembly, so that the narrow beam passing through the slit will reflect off different parts of the diffraction grating and be received by the video camera in a scanning mode. As a result, this single device will cover a wide field of view across the range of spectra in a short duration of time. In fact it can obtain a spectrum of 3 × 3 degrees of sky in one second.
Heterojunction bipolar transistor characterization using noncontact optical spectroscopy
Martin E. Murtagh, Patrick Kelly, Breda O'Looney, et al.
In this work we report the application of optical spectroscopic techniques namely photoreflectance (PR), ellipsometry and photoluminescence (PL) for qualification of InGaP/GaAs multi-layer heterojunction bipolar transistor (HBT) material. These techniques reveal important information regarding the quality of the different InGaP and GaAs layers for the emitter, base, collector and surface cap regions. In particular PR studies of non-optimal HBT material reveals InGaP (emitter) layer sub-lattice ordering effects, as correlated with selective area electron diffraction patterns. Moreover, comparison of the emitter/base interface field levels and InGaP ordering data reveals further evidence of a non-abrupt InGaP/GaAs heterojunction, proving to have adverse consequences for HBT current gain characteristics and consistent with measured reduced common emitter current gain. Supporting evidence for such non-optimal, strained emitter/base region is provided from x-ray (004) & (002) diffraction but mainly from cleaved edge (g=002) dark field TEM, revealing significant interfacial non-uniformity, also likely correlated to the emitter layer ordering present. PR spectral information is compared with PL lineshape data - including Arrhenius (thermal) plots, while extracted interfacial electric field data are also supported by device finite-element (ANSYS) modelling. In summary this paper demonstrates the application of non-destructive and rapid techniques for evaluation and control of compound semiconductor materials for HBT technology.
Session 31
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Optical sensing systems for primary-level science education
Adam Markey, Bernard Tyers, Roderick Shepherd, et al.
In the last three years, a number of Irish primary schools have been using LEGO Mindstorms technology in order to investigate the use of project-based learning as an alternative teaching tool. This has involved the use of LEGO bricks combined with standard electronic motors and some commercial sensors (e.g. temperature). In order to develop this project into the area of science education, we have developed a range of miniaturized optical sensors, which are compatible with the LEGO platform. This paper describes two such sensors that have been developed and fabricated for use with the LEGO platform, a collaboration between the MIT Media Lab and the National Centre for Sensor Research. In particular a working oxygen sensor has been designed and fabricated. The principal design features were compatibility with the programmable LEGO platforms and robustness for classroom use. This sensor uses the method of intensity quenching to determine oxygen concentration. In addition, simple color sensors have been produced. The aim of developing such sensors is to familiarize students with the concept of colour detection and to introduce them to the basic principles of spectroscopy. The performance of both sensor types and preliminary classroom results are reported.
Problem-based learning: an approach to enhancing learning and understanding of optics for first-year students
Brian W. Bowe, Siobhan Daly, Cathal Flynn, et al.
In this paper a model for the implementation of a problem-based learning (PBL) course for a typical year physics one programme is described. Reference is made to how PBL has been implemented in relation to geometrical and physical optics. PBL derives from the theory that learning is an active process in which the learner constructs new knowledge on the basis of current knowledge, unlike traditional teaching practices in higher education, where the emphasis is on the transmission of factual knowledge. The course consists of a set of optics related real life problems that are carefully constructed to meet specified learning outcomes. The students, working in groups, encounter these problem-solving situations and are facilitated to produce a solution. The PBL course promotes student engagement in order to achieve higher levels of cognitive learning. Evaluation of the course indicates that the students adopt a deep learning approach and that they attain a thorough understanding of the subject instead of the superficial understanding associated with surface learning. The methodology also helps students to develop metacognitive skills. Another outcome of this teaching methodology is the development of key skills such as the ability to work in a group and to communicate, and present, information effectively.
Maintaining the technological edge through local workforce collaboration
Martha M. Finnegan, Celine Haugen
Napa County California has been a pioneer in Industry Cluster Analysis and has worked with a wide variety of industries to resolve identified needs with economical and achievable solutions. The Napa Workforce Investment Area has developed practical approaches to generate sustained interest from students and has incorporated this into its routine services thereby insuring a continuous supply of new practitioners and reducing costs to business. Career development, linking students directly with specific businesses and industries as well as tuition assistance have been provided to insure the continuation of a highly skilled workforce within the region. Letting industry set the agenda in problem solving forums has proved a valuable tool in resolving workforce retention and skill upgrade issues as well. A result of this collaborative effort has been the development of new curriculum and the opening of new Industry Schools to meet industry needs for training and retraining workers for new occupations within industries. In order to assist the various industries and individual businesses to meet changing technology and retention needs, Napa provides skill upgrade training to incumbent workers at no or reduced costs to businesses. Extending these practices to the field of Photo Optics is now a matter of formula.
Graduate and professional development in imaging and optical signal processing, and related fields
Jonathan George Campbell, Fionn D. Murtagh, Munevver Kokuer
Image processing, signal processing and computer vision are increasing in importance, and are indeed slowly being considered as core competences in computer science. The specification of computing curricula by the ACM and the IEEE Computer Society states that technical advances over the past decade have increased the importance of topics such as graphics and multimedia, and considers as a core topic Graphics and Visual Computing. With the advent of courses in digital media in electrical engineering and computer science, the increasing importance of computer imaging and vision is manifest, and not only in electrical engineering and computer science departments. The need for development and training of research students is more often than not badly catered for at the present time in Irish universities (Republic, Northern Ireland). Research students are often from diverse discipline and educational system backgrounds. A characteristic of a dynamic and effective graduate and research student environment is not just the raw numbers of PhDs produced, but also relative consensus on the part of the 'community' on the most effective major directions of innovation and of focus. On any such qualitative characteristic, Irish universities, institutes of technology and research institutes are not performing well. Successful models for such community-strengthening include doctoral networks at European level, and summer schools at national or regional level. This paper addresses specific issues: (i) the means by which the needs for graduate research level community-strengthening in the areas of signal processing, and image processing and computer vision, can be satisfied; (ii) what the most crucial elements of these fields are, i.e. proposed key areas and curricula.
Optics education within engineering at University College Dublin
John T. Sheridan, Gerald Byrne, Patrick Connolly, et al.
Undergraduate students within many of the departments which make up the Faculty of Engineering and Architecture at University College Dublin meet optics, optical inspection techniques and opto-electronics at various times during their standard four year undergraduate degree course. As well as optics fundamentals taught as part of their physics courses, engineering courses specifically concerning optics and opto-electronics are available. Furthermore many graduate students are involved in either projects, which are completely optics based, or carry out research projects involving the use or development of specific optical instruments. These projects include the development of image processing capture and processing software, high power laser machining of materials, design and testing of lasers for fiber optic telecommunication and sensing applications and photochemistry. In this paper we offer a brief review of some of the main optical educational themes covered within our faculty and present some details regarding a few optics based postgraduate research projects.
New insights from the cutting edge
The paper explores some lessons for third-level electronic engineering education based on the experience of an engineer who has migrated from electrical and electronic engineering into telecommunications. An introduction in telecommunications began in Queens University of Belfast B.Eng studies. A PhD course in the Optoelectronics Department of Strathclyde University followed investigating novel methods of equalising the output of erbium-doped fibre devices. The experience and technical knowledge gained helped obtain employment at Kymata Limited working in R&D. This career path may be typical of a new generation of electronics engineers. The first part of the paper explores the limitations and advantages of professional development outside of a planned educational programme in telecommunications. The second part of the paper describes the excellent optics R&D development base of Scottish Universities that offer a model perhaps for Ireland and the rest of the world. In this competitive age the time taken to bring a device to production specifications can be critical to the on-going survival of small companies. The paper ends by attempting to tie together a number of strands in an overview that may help develop the ongoing debate into the evolution of electronic engineering in third level education.
Impact of computational methods in optical design education
This paper describes our approach in providing graduate-level training in optical design and in the use of optical design software.
Poster Session
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Out of the sun: the evolution of optical engineering programs in Carlow and Essex from 1979 to 2002
Norman Douglas McMillan, L. Vallely, K. Kelly, et al.
This paper analyses the evolution of courses in the Institute of Technology Carlow (formerly the Regional Technical College) in physics, optics, photonics, instrumentation and optoelectronics from 1979. Notably, these course developments culminated in the fist specialist optoelectronic Honours degree in the UK or Ireland, which ran with outstanding success for over a decade under the umbrella of the University of Essex. In the last year, the first specialist degree in Optical Engineering to appear perhaps indeed in Europe has been launched. All these development of Irish optics education have been achieved against unresponsive national and institutional policies framed by a severe reluctantly to accept the need for technical manpower outside of the established disciplines. Other associated optical course innovations of the 'Computer Networking and Optical Communications' National Certificate/Diploma and then subsequently 'Networking' degree course have developed in Carlow exclusively on the basis of the photonics diploma material and contain large element of optical fiber telecommunications/photonics material. The exciting Carlow odyssey is however just beginning as can be seen by the preparation of a further new degree in Optical Engineering Design. This course it is hoped will comprehensively address the issues of training manpower for optical device and system engineering.
Design from chaos: applying data entropy methods for complex system design
Kevin Tiernan, Sven Riedel, Norman Douglas McMillan, et al.
The paper critically assesses and illustrates the use of the data entropy budget method in both product and systems engineering based on the experience of developing an optoelectronic instrument known as the tensiograph. The design of such a system involving optoelectronic, electronic, thermal, mechanical, chemical and data processing noise components presents difficult engineering problem from the complex of noise spectrum contributions. This project provides perhaps an important case study for optical engineers because it was developed over a period of 15 years. The design history recorded in the data entropy-time graph, shows clearly the step-wise improvements achieved from the various engineering efforts. The present 11-bits information content of the instrument, with impressive signal-to-noise ratio exceeding 1000:1, was developed from prototype with less than 3-bit resolution. The paper concludes with an assessment of the relevance of this method to optical engineering in which a diverse number of technologies are frequently integrated in products and systems. Finally, the role of data entropy methods in third level education is then briefly considered with very clear lessons drawn from the foregoing concrete example offered by this case study.
Postgraduate training in the field of optics: a case study
Andreas T. Augousti, Francois-Xavier Maletras, Julian Mason
The progress of a PhD in Optical Instrumentation is examined as a case study of an example of postgraduate training in the area of optical instrumentation. The work itself is concerned with the further development of the Fibre Optic Resipratory Plethysmograph (FORP), in order to improve respiratory detection and permit cardiac response detection. Issues relating to skill mix development are examined.
Teaching optics to engineers
The challenges of teaching optics and optoelectronics in a broad based Engineering school will be discussed. At Liverpool John Moores University, optical devices and optoelectronics is taught from the second year of degree courses right through to MSc level. At second year, students in Broadcast Technology, Applied Electronics have little physics background and are more interested in networks than basic devices and fundamentals of light. Even at MSc level, students' backgrounds are patchy. The challenge is to get across the basic principles in an interesting way, and excite students' interest by focusing on state of the art, current developments and applications. This is backed up with demonstrations and student projects attached to active research groups. Research groups in the school contribute to teaching in their fields. Members of the Coherent and Electro-optics Research Group teach "Optics and Imaging in Medicine". Members of the Optical Fibre Sensors Research Group teach "Optoelectronics" and "Analogue and Optical Devices". Also discussed are the challenges of teaching Physics students optoelectronics, and the decline of the "Optical Science and Technology" degree course, due to falling student numbers and the decline of physics and physics based courses in the UK.
Session 24
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Review of past, present, and the future of recording technology
Abdul-Rahman Al-Jibouri
The revolution of information storage and recording has been advanced significantly over the past two decades. Since the development of computers in early 1950s by IBM, the data (information) was stored on magnetic disc by inducing magnetic flux to define the pit direction. The first disc was developed by IBM with diameter of 25inch to store around 10 kByte. After four decades, the disc drive has become more advanced by reducing the drive size, increasing ariel density and cost reduction. The introduction of new computer operating systems and the Internet resulted in the need to develop high ariel density in the 1990s. Therefore, the disc drive manufacturers were pushed harder to develop new technologies at low cost to survive the competitive market. The disc drives, which are based on media (where the data/information is stored) and the head (which will write and read data/information). The head and disc are separated and with the current technology the spacing between the disc and head is about 40nm. A new technology based on magnetic recording was developed to serve the audio market. This technology is called magnetic type, it is similar to the disc drive, but the media is based on tape rather than rigid disc. Another difference being the head and media are in direct contact. Magnetic tape was developed for audio application and a few years later this technology was extended to allow and accept another technology, called video. This allows consumers to record and view movies in their home. The magnetic tape also used the computer industries for back up data. Magnetic tape is still used in computers and has advanced further over the past decade, companies like Quantum Corp has developed digital linear tape.
Case Studies and Panel Discussion
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From creative partnerships to innovative developments
Creative partnerships have the potential to accelerate developments for innovative products. A clear understanding between creative partners in optotechnologies from the generating of ideas to developing the technology can produce successful results. This senario is being applied by a creative partnership with an arrangement between three companies: one in Ireland, one in Scotland and the other in the USA. This has resulted in the production of beta and proof-of-concept models for a range of 4D volumetric imaging systems suitable for a wide range of applications developed over a short period of time.
Poster Session
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Evaluation of different signal processing algorithms in laser Doppler perfusion measurements
The Laser-Doppler (LD) method is extensively used in clinical experiments for microcirculation measurement. The results of LD perfusion measurements depends on technical factors such as laser light wavelength, LD probe arrangement, and signal processing algorithm. The aim of this study is to compare the output of various signal processing algorithms (LDP) with the use of digital spectral analysis of the photodetector current. Comparison is made with the output of a commercial LD instrument (LDF). The results obtained using a simple one-tube physical model confirm that the best linearity of response of the LD instrument for changes of flow velocity is given by the algorithm based on first moment of power spectral density of AC component of photodetector's signal.
Developments in laser Doppler blood perfusion monitoring
Martin J. Leahy, Frits F. M. de Mul, Gert E. Nilsson, et al.
This paper reviews the development and use of laser Doppler perfusion monitors and imagers. Despite their great success and almost universal applicability in microcirculation research, they have had great difficulty in converting to widespread clinical application. The enormous interest in microvascular blood perfusion coupled with the 'ease of use' of the technique has led to 2000+ publications citing its use. However, useful results can only be achieved with an understanding of the basic principles of the instrumentation and its application in the various clinical disciplines. The basic technical background is explored and definitions of blood perfusion and laser Doppler perfusion are established. The calibration method is then described together with potential routes to standardisation. A guide to the limitations in application of the technique gives the user a clear indication of what can be achieved in new studies as well as possible inadequacy in some published investigations. Finally some clinical applications have found acceptability and these will be explored.
Luminescent characteristics of sol-gel-produced zinc sulphide display structures
Yvonne M. Kavanagh, David C. Cameron, Brendan Ryan, et al.
Thin film electroluminescent (TFEL) display structures have been produced by sol-gel technology, with the active layer comprising doped zinc sulphide films produced by the sulphidation of sol-gel deposited zinc oxide thin films. The luminescent properties of display structures using manganese-doped zinc sulphide, which has a strong orange emission due to the Mn2+4 T1(4G) 6A1(6S) transitions have been investigated using photoluminescence (PL), cathodoluminescence (CL), and electroluminescence (EL) and the correlation between the luminescence produced by the various methods has been studied. A comparison of the spectra using PL, CL and EL has shown how these excitation methods can be used to quantify the electroluminescence produced by the zinc sulphide. The effects of the interaction between the insulating layer and the emission layer have also been studied.
Thermal reliability studies of optoelectronic components
Padraig J. Hughes, Ger Healy, Xavier Llinares, et al.
For optical networks, the operating life of optoelectronic components is expected to be over 20 years. Network designers therefore require components, which have been reliability tested in accordance with assured protocols, such as Telcordia Generic Reliability Assurance Practices (BellCore). In this paper, we report on the development of a system for thermal reliability studies of optoelectronic devices. The system incorporates an environmental test chamber programmed to provide differing temperature environments in the range (-180° to 300° C) as well as constant bias current or voltage to the device udner test. Case studies for preliminary screenign and temperature cycling tests on a wide range of novel active and passive devices fabricated at NMRC for short-haul networks markets are assessed and reported using this system.
Accuracy of laser cutting and its influence on the mechanical behavior of stents
Carine Gachon, Patrick Delassus, Peter McHugh
A coronary stent is a mechanical device designed to open arteries that have been occluded. The manufacturing of stents involves the laser-cutting of specific designs in stainless steel tubes. In order to determine the mechanical behaviour of stents, tensile tests are performed on straight beams. The tensile test specimens are laser-cut into the same tubes as used in the manufacturing of stents. The hardening curves obtained show that the yield stress increases when the width of the struts decreases, whereas the breaking point increases when the width increases. In order to understand this phenomenon, the role of laser-cutting is investigated. Firstly, it is shown that the heat-affected-zone, associated with laser-cut items, is very small compared to the size of the specimen. Therefore, the influence of the heat-affected-zone is considered as negligible. The inaccuracy of laser-cutting is then studied by measuring a succession of straight beams. A difference in width between the two extremities of the strut is observed. The error increases when the width of the beam decreases. An F.E.A analysis of the tensile test shows a stress concentration at the smaller extremity, explaining why the true strain at breaking point decreases with the width of the struts.
Development of an optical electronics curriculum for electrical and electronic engineers
This paper describes the present status and the ongoing development of a curriculum for providing a broad, but substantive introduction to optical electronics for senior undergraduate Electrical and Electronic Engineering students. An outline of the current course structure is presented, along with the rationale for the topics included and the order in which they are taught. The methods of course delivery are evaluated and their effectiveness is discussed along with techniques for maintaining student attention and interest. Other teaching innovations, aimed at encouraging postgraduate studies in optoelectronics/photonics, include presenting topics from the optoelectronics research within the Department and offering a broad selection of final year undergraduate projects in optical electronics and photonics. To promote interest in pursuing optical electronics and photonics as a career an optical engineering professional is invited to present a guest lecture during the course. The evolution of a teaching portfolio and self-assessment, in addition to student criticism and evaluation are described. Future directions for this course are outlined, in particular the development of class-based demonstrations to enhance student learning and material comprehension.
New autofocusing system for laser micromachining
Marc Nantel, Kevin Sue-Chu-Lam, Dejan Grozdanovski
We present a new feedback system to keep laser machining beams in focus at the workpiece surface. This autofocus device is especially desigend wiht laser micromachining in mind, with direct monitoring of the laser focus spot are. It is a non-contact, non-capacitive method relying on the interpretation of video image signals. The autofocusing system functions by imaging a laser line which is projected down on a 45-degree angle onto the surface which is being machined. If the surface deflects up or down, the laser line moves corresondingly in the horizontal plane; this change can be monitored on the imaging system and processed by the autofocusing electronics. The use of a line instead of a small spot of light prevents unexpected 'dives' from the auto-focus laser hitting an already-cut hole. A volage setpoint is produced for feedback to the vertical micropositioning stage controller to move the stage and correct the focusing lens position. Curved or otherwise non-flat workpieces are shown to be precisely machined without prior knowledge of their exact shape.
Electrochromic paper-quality displays
Colm McAtamney, Francois Pichot, Aoife O'Flaherty, et al.
In this paper we give an overview on NTera's novel reflective display technology with real 'ink-on-paper' readability. Our technology is based on mesoporous wide-bandgap semiconductor films modified with self-assembled monolayers of electrochromic chromophores. The direct vicinity of each electrochromophore to the semiconductor allows its electronic addressing in the millisecond domain. The high molar extinction coefficient of the organic chromophores in conjunction with the extremely large specific surface area of the mesoporous semiconductor substrate allows to achieve deep colorations with high contrast ratios. Combined with a unique white reflector technology yielding reflectivities above 50 percent and excellent angular contrast independnece, oru displays show outstanding optical properties, comparable to those of ink on paper. Applying simple printing techniques these displays can be manufactured from commercially available nanomaterials like TiO2 or other doped or undoped metal oxides. Along with favorable electronic properties like low power consumption and excellent open-circuit memory electrochromic displays seriously rival conventional LCD display applications.