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- Remote Sensing of Targets and Backgrounds
- Lasers, Nonlinear Optics, and Quantum Electronics
- Optical Engineering
- Optical and Image Processing
- Lasers, Nonlinear Optics, and Quantum Electronics
- Optical and Image Processing
- Holography, Micro-Optics, and Diffractive Optics
- Lasers, Nonlinear Optics, and Quantum Electronics
- Optical Engineering
- Optical and Image Processing
- Lasers, Nonlinear Optics, and Quantum Electronics
- Optical Materials
- Lasers, Nonlinear Optics, and Quantum Electronics
- Industrial and Medical Applications
- Holography, Micro-Optics, and Diffractive Optics
- Fiber Optics and Communications
- Remote Sensing of Targets and Backgrounds
- Industrial and Medical Applications
- Lasers, Nonlinear Optics, and Quantum Electronics
- Holography, Micro-Optics, and Diffractive Optics
- Remote Sensing of Targets and Backgrounds
- Optical Materials
- Lasers, Nonlinear Optics, and Quantum Electronics
- Remote Sensing of Targets and Backgrounds
- Holography, Micro-Optics, and Diffractive Optics
- Fiber Optics and Communications
- Industrial and Medical Applications
- Lasers, Nonlinear Optics, and Quantum Electronics
- Holography, Micro-Optics, and Diffractive Optics
- Optical Engineering
- Industrial and Medical Applications
- Remote Sensing of Targets and Backgrounds
- Fiber Optics and Communications
- Optical Engineering
- Lasers, Nonlinear Optics, and Quantum Electronics
- Remote Sensing of Targets and Backgrounds
- Optical Materials
- Remote Sensing of Targets and Backgrounds
- Lasers, Nonlinear Optics, and Quantum Electronics
- Optical Materials
- Industrial and Medical Applications
- Fiber Optics and Communications
- Holography, Micro-Optics, and Diffractive Optics
- Lasers, Nonlinear Optics, and Quantum Electronics
- Industrial and Medical Applications
- Optical Materials
- Lasers, Nonlinear Optics, and Quantum Electronics
- Holography, Micro-Optics, and Diffractive Optics
- Remote Sensing of Targets and Backgrounds
- Lasers, Nonlinear Optics, and Quantum Electronics
- Holography, Micro-Optics, and Diffractive Optics
- Optical Materials
- Remote Sensing of Targets and Backgrounds
- Optical and Image Processing
- Lasers, Nonlinear Optics, and Quantum Electronics
- Optical and Image Processing
- Lasers, Nonlinear Optics, and Quantum Electronics
- Fiber Optics and Communications
- Remote Sensing of Targets and Backgrounds
- Optical and Image Processing
- Remote Sensing of Targets and Backgrounds
- Optical Materials
- Industrial and Medical Applications
- Remote Sensing of Targets and Backgrounds
- Holography, Micro-Optics, and Diffractive Optics
- Optical and Image Processing
- Fiber Optics and Communications
- Remote Sensing of Targets and Backgrounds
- Optical Engineering
- Holography, Micro-Optics, and Diffractive Optics
- Optical Engineering
- Lasers, Nonlinear Optics, and Quantum Electronics
- Optical Materials
- Fiber Optics and Communications
- Remote Sensing of Targets and Backgrounds
- Lasers, Nonlinear Optics, and Quantum Electronics
- Fiber Optics and Communications
- Optical Engineering
- Fiber Optics and Communications
- Optical Engineering
- Additional Papers
Remote Sensing of Targets and Backgrounds
Optical remote sensing of atmospheric total ozone with radiometers
Show abstract
A high-spectral resolution radiometer and a Volz sunphotometer have been in operation to monitor solar irradiance in the visible region 0.4 micrometers 0.7 micrometers , and at five discrete wavelengths covering the visible and near IR regions, respectively, since November 1993 at the Indian Institute of Tropical Meteorology, Pune, India. Using the spectroradiometer-derived spectral variation of total optical depth in the Chappuis-band, ozone content in the atmospheric column was estimated by following the multiple regression method. Total ozone content in the atmosphere was estimated by following the multiple regression method. Total ozone content in the atmosphere was also determined by using the differential absorption of solar radiation at two wavelengths in and around the Chappuis-band from the sunphotometer observations. The observations carried out on about 200 cloud-free days spread over the period from February 1993 to May 1996 were used in the study. A comparison of total ozone, thus retrieved by the Chappuis- band method differed from the Dobson spectrophotometer measurements by about +/- 20 percent on the most stable days. These differences can be attributed to a combination of large aerosol optical depths, diurnal variation of aerosol optical depth, the deviation from the assumed power law relationship coefficients. The ozone optical depths inferred experimentally from the Chappuis-band method have been used to determine more accurate aerosol optical depths as compared to those routinely to those routinely obtained by using model ozone vertical profiles.
Lasers, Nonlinear Optics, and Quantum Electronics
Dynamic compensation of thermal lensing and birefringence in a high-brightness Nd:Cr:GSGG oscillator
Show abstract
In this work, five fundamental concepts were combined to a low development of high efficiency, low divergence, narrow bandwidth, flashlamp pumped oscillators capable of operation over a broad operating range. These concepts were: flashlamp pumped Nd:Cr:GSGG to achieve high efficiency, a 'Reentrant Cavity' to eliminate birefringence losses, a variable radius back mirror in a hemispherical cavity to achieve maximum Gaussian beam fill factor, a very high damage threshold, spectrum narrowing output coupler fabricated using a stack of uncoated etalons to form a resonant reflector, a cylindrical zoom lens to completely eliminate astigmatism. The results were successful, and yielded an oscillator that produced 10 mJ, TEM00 300 MHz bandwidth, 75 ns pulses, over a repetition rate of 1-20 Hz, and at a slope efficiency of 2 percent. These techniques were also successfully applied to a YLF oscillator. They may, in part, be adapted for use to unstable resonators.
Optical Engineering
Gradient-index design example for a variable eyepiece
Konrad Seil
Show abstract
Special features and limitations of a conventional variable eyepiece design and a gradient-index design example are compared. Optical performance and manufacturing aspects are discussed. The influence of gradient-index lenses on the different aberrations is shown. A rough cost estimation of both -- classical and gradient-index design -- is presented.
Optical and Image Processing
Exploitation of incoherent source for partially coherent processing
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In this paper we show that temporal and spatial coherence can be exploited from an incoherent source for complex amplitude processing. The method is by dispersing the spectral content and spatially encoding the incoherent source such that high temporal and desired spatial coherence can be obtained. To confirm our argument, experimental demonstrations are provided.
Lasers, Nonlinear Optics, and Quantum Electronics
Numerical investigation on intensity-dependent energy transfer and beam fanning in high-gain photorefractive BaTiO3 crystal
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The numerical investigation uses the intensity-dependent gain coefficient in a coupled-wave formulation which explains nonlinear intensity-dependent behavior associated with the growth of beam-fanning observed in a photorefractive BaTiO3 crystal. The study shows the effect of crystal orientation and biasing illumination on such a nonlinear behavior.
Optical and Image Processing
Performance study of binary and real-valued joint-transform correlators in the presence of noisy input scene and poor illumination
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The correlation performances of four different types of joint- transform correlators (JTCs) are investigated in a non- cooperative situation when the target image is cluttered with scene noise and present under poor illumination condition. Computer simulation and experimental results are provided. The JTC based on modified fringe-adjusted filter performs better in such a combined situation.
Planar optical correlator with coherent light
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A compact planar configuration for performing optical correlation is described. It is comprised of two pairs of identical holographic lenses and a holographic filter. Each pair of lenses is recorded on a single substrate and together perform exact Fourier transformation. The light between the lenses propagates inside the substrate by means of total internal reflection. The design and recording considerations for each of the lenses along with experimental results for the overall planar correlator are presented.
Holography, Micro-Optics, and Diffractive Optics
Iterative calculation, manufacture, and investigation of DOE forming unimodal complex amplitude distributions
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We present results of iterative calculation, manufacturing and experimental as well as theoretical investigations of a novel diffractive optical element (DOE) which transforms a Gaussian TEM00 input beam into a unimodal Gauss-Hermite (1,0) complex amplitude distribution. The iterative calculation procedure is based on the application of the method of generalized projections. The projection operator onto a set of modal functions is implemented through partition of the focal plane into a 'useful' and an 'auxiliary' domain. To improve the error reduction during the iterative calculation procedure, a stochastic predistortion in the auxiliary domain is chosen. This calculation results in a 2-D phase distribution which has to be transferred into an optical element. This element has been manufactured as a 16 level surface profile by (variable dose) electron-beam direct- writing into a PMMA resist film and a subsequent development procedure of the resist. Each of the generated 15 steps of the resist profile corresponds to a certain electron dose, comparable to a usual 'isobathic process' or a 'monotone etching method.' The final element consists of a fused silica substrate coated with the structured PMMA film. Both computational and experimental results are presented and demonstrate a good conformity with each other. Energy efficiency has been measured in the focal plane as 37.7%, compared with the calculated value of 45.5%. The achieved results show good prospects of such an approach for the formation of unimodal distributions.
Lasers, Nonlinear Optics, and Quantum Electronics
Design of low-threshold narrow-linewidth optical parametric oscillators
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A demonstration of narrow linewidth, low threshold OPO is presented. Two basic line-narrowing methods are applied. One method employs an intra-cavity grazing incident grating, and compensates the high losses caused by the grating by adding a laser gain element to the cavity. In the second method, a single element birefringent filter with low insertion loss is introduced in the cavity. Both configurations allow an efficient, compact design of tunable source with low pump threshold and narrow linewidth.
Optical Engineering
Fast large-area low-cost two-dimensional optical position sensor
D. Avtabi,
E. Burstein,
Aryeh M. Weiss
Show abstract
A novel two dimensional optical position sensor based on confinement of luminescence within a flat panel is described. The basis of the sensor is a flat luminescent panel, such as those used in luminescent solar energy concentrators. In these concentrators, a glass or plastic plate is either coated or impregnated with a fluorescent material. The incident radiation produces luminescent emission, much of which is confined within the plate through total internal reflection, and is thus guided to solar cells which line the thin edges of the plate. In order to use such plates as a position sensor, four photodiodes are placed along two orthogonal axes at the edges of the plate, and the plate is illuminated with a spot of light. The spot of light induces luminescence, which is detected by the four photodiodes. The photodiodes' output is processed to provide position information. Large area position sensors based on the above idea were constructed, using fluorescent plexiglass which was obtained from commonly available fluorescent clipboards. The photodiode output was combined using a self-normalizing function to eliminate sensitivity to non-uniformity in the optical characteristics of the fluorescent plates. This paper presents the results obtained to date, together with suggestions for further improvement in the sensor based on these results.
Optical and Image Processing
Compact updatable optical correlator
Doron Malka,
Silviu Reinhorn,
Yaakov Amitai,
et al.
Show abstract
A compact configuration for a real-time updatable optical correlator is considered. The correlator is designed to operate with incoherent illumination and efficient phase filters, which can be implemented with real-time, updatable, electronically addressed, liquid-crystal spatial light modulator. In order to obtain both a rigid and a compact correlator, a configuration which can be incorporated with planar optics is investigated. The overall correlator includes two pairs of diffractive lenses, each for performing a Fourier transformation, one spatial light modulator and input and output interface devices. The design consideration and fundamental limits of a compact updatable correlator using off-axis, diffractive lenses are presented, along with some experimental results.
Lasers, Nonlinear Optics, and Quantum Electronics
Comparison between rod and slab architectures for high-power diode side-pumped Q-switched Nd:YAG lasers
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A comparison between two side-pumping configurations of Nd:YAG Q-switched lasers is presented, based on experimental results and theoretical models developed by us. The first architecture, experimentally and theoretically tested, used a close-coupled pumping design where bare diode lasers were placed next to a Brewster cut rod. This laser produced 10 W average power at 10 kHz repetition rate with 30 ns pulse width and good beam quality, 12 percent light to light conversion efficiency was achieved with the added advantage of simplicity. The second arrangement, theoretically tested, was a zig-zag slab layout where the diode light was collimated with micro-lenses prior to being absorbed in a strip like are inside the slab. This design eliminated the problem of thermal induced birefringence, through the Cartesian symmetry of the thermal gradients developed inside the slab, while averaging out pump nonuniformities through the zig-zag path, thus yielding high beam fill factor within the pump volume.
Optical Materials
Photoacoustic spectroscopy of photovoltaic materials
M. A. Slifkin,
L. Lurie,
Aryeh M. Weiss
Show abstract
A photoacoustic spectrometer is described which has been constructed to measure the spectra of photovoltaic materials in the ultra violet, visible and near infra red regions. The range of this photoacoustic spectrometer is from 0.3 to 1.8 micrometers. This technique has the advantage of being non- intrusive and non-destructive. Measurements have been made of a variety of photovoltaic materials, including a CdS/CuIn1- xGaxSe2 heterojunction and an InP/InGaAsP quantum well layer system. Bands arising from intrinsic impurity subgap levels were observed beyond the band edges.
Advanced materials for high-density optical storage
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High storage density optical disk is expected as the key device for storage at the dawn of the full-scale multimedia age. It meets the requirement of a large storing capacity to record and retrieve great amounts of data including motion pictures, audio information and data for computer processing. The advanced storage media are the most important means for high density optical disk storage. According to optical diffraction limitation the diameter of the focused spot is proportional to (lambda) /NA, where (lambda) is writing and reading laser wavelength and NA is optical numerical aperture of focusing lens. Therefore, the practical approach for minimizing the mark length is to decrease (lambda) and to increase NA. There are three steps for decreasing laser wavelength from 780 - 800 nm used now to 630 - 650 nm (red diode lasers) and then to 400 - 500 nm (blue-green lasers). The advanced storage materials should be sensitive, stable and with recording performances at 630 - 650 nm and 400 - 500 nm laser wavelength regions. This paper reports our progress of three kinds of advanced storage materials for high density optical disks, there are: magneto-optical, phase change and organic storage materials. The main attention is put on rewritable (erasable) optical storage.
Lasers, Nonlinear Optics, and Quantum Electronics
Physics and technology of tunable laser crystals
Peizhen Deng
Show abstract
Solid state tunable laser crystal can play a much more important role than liquid dye in ultrafast laser, and probably in high power lasers. In this paper, the recent progress in our laboratory on the tunable laser crystals containing paramagnetic ions such as Ti3+ of 3d1 configuration and Cr4$PLY of 3d2 configuration, are reported here. In the case of the former, two new techniques have been invented to produce high quality Ti-doped sapphire crystal, they named by induction field up-shift method (IFUM) and temperature gradient technique (TGT), which differ from the traditional Czochralski Method and heat exchange method. The high merits of IFUM and TGT Ti:Al2O3 crystals have been demonstrated, and especially the laser operations have been performed very well by using them. In the latter case, the special attention of our laboratory has been paid on the recent experimental results of quadravalent chromium ion doped near-IR tunable laser crystals, which include YAG, forsterite, and also some new laser hosts such as SGGG, and LGO, etc. Their spectroscopy and laser characteristic have also been discussed.
Industrial and Medical Applications
Photodynamic damage to cartilage and synovial tissue grafted on a chick chorioallantoic membrane
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Rheumatoid arthritis (RA) is a chronic inflammatory disease of the synovial joints causing pain deformities and disability. The highly vascular inflamed synovium has aggressive and destructive characteristics, it invades, erodes and gradually destroys cartilage and underlying bone. Photodynamic therapy (PDT) was performed using the chick chorioallantoic membrane (CAM) model to investigate the vitality of synovium and cartilage implanted on the CAM. Synovium, obtained from human patients, was grafted onto the CAM; gross microscopy and histology proved its vitality 7 days post grafting. Cartilage obtained from rabbit knee joint was also maintained on the CAM for 7 days. Its vitality was demonstrated by histology and by measuring metabolic and enzymatic activity of cartilage cells (chondrocytes) as well as the collagen and proteoglycans content. Selective PDT was performed using aluminum phthalocyanine tetrasulfonate (AlPcS4), a hydrophilic compound, soluble in biological solutions, as a photosensitizer. After irradiation with a diode laser (lambda equals 670 nm, 10 mW) damage was observed in vascularized synovium grafts, whereas avascular cartilage remained intact.
Holography, Micro-Optics, and Diffractive Optics
Gradient method for the design of multiorder diffraction gratings using the Rayleigh method
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A method for the design of perfectly conducting multiorder diffraction gratings is proposed. The design uses the Rayleigh method and is based on the gradient search algorithm for optimization of grating structure from the condition of the generation of a desired array of diffraction orders. The developed algorithm is more general and for d >> (lambda) , where d is the grating period and (lambda) is the wavelength of incident light, goes over into the familiar gradient algorithms for designing gratings in the Kirchhoff approximation. The designs of multiorder gratings with equal order intensities are reported with the efficiency of more than 90% and root-mean square errors of 2 - 7%.
Fiber Optics and Communications
Multiterabit per second ATM interconnection through optical WDM
Dan Sadot,
Adisak Mekkittikul
Show abstract
Optical switching of Tbit/sec ATM streams through dynamic WDM is proposed. Optical manipulations are concentrated in a small area, overcoming technological obstacles. Central control is avoided via optical carrier detection. Multimedia and parallel computing applications are supported.
Remote Sensing of Targets and Backgrounds
Light propagation through multilayer atmospheric turbulence
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A new treatment is presented for light propagation through multilayer turbulence. Equations for the intensity and phase of an observed wavefront re derived together with their validity conditions for both single and multiple layer systems. A method for finding the statistics of observed scintillations is presented together with a detailed calculation for a single layer system.
Industrial and Medical Applications
Surface feature investigation using the optically measured sliding window spectrum
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In this work we present a method to investigate surface features based on the scanning of a focused beam over the surface and the interpretation of far field data. It is shown that the measured data is the sliding window spectrum (SWS) of the surface. Inspection of the SWS can be used to identify different surface features, and to perform high precision measurements for certain surface structures. By sampling adequately the SWS we measure the amplitude of the surface Gabor expansion coefficients and build the Gabor diagram. A projection onto constraint sets (POCS) algorithm is used to reconstruct the surface from the Gabor diagram. The constraints are provided by the physical characteristics of the surface and by the far field measurements. The projections between the constraint sets are implemented using the Gabor transform theory. Computer simulations and experimental results show that this method can reconstruct accurately shallow phase objects.
Polarization vision: a door to an unseen world
Nadav Shashar
Show abstract
Polarization vision (PV), or the sensitivity to the partial polarization and orientation of polarization of partially linearly polarized light (PLPL), is widely spread among marine animals. Humans however are mostly insensitive to polarized light and therefore the information it carries is not readily available to us. Using an imaging polarizer, capable of analyzing the linear polarization characteristics of a full image on a single pixel basis, I studied the distribution of PLPL in various oceanic environments, its reflection from various surfaces, and its use by marine animals. The polarimeter was based on two twisted nematic liquid crystals and a fixed polarizing filter in series in front of a video camera. Results revealed a great complexity in the marine polarized light environment. Further, several animals such as fish, echinoderms, and crustaceans reflected unique polarization patterns. In the horizontal line of view, the background light is more than 30% horizontally polarized. Under these conditions, transparent targets, which depolarize or rotate the orientation of polarization are expected to be conspicuous through PV. Several species of zooplankton were found to depolarize light in such a fashion. In field measurements PV enabled an increase of more than 80% in detection range for transparent depolarizing targets over intensity imaging.
Lasers, Nonlinear Optics, and Quantum Electronics
Mixed states: children of quantum mechanics with nonquantal behavior
Michael Brieger
Show abstract
The established notion of angular momentum coupling is shown to be incomplete. Using diagonalization most existing theories try to understand the dynamics of angular momentum coupling by concluding form the stationary aspects they cover. Missing the insight into the real dynamics they fail to correctly interpret the most general wave functions that are obtained from superpositions of, e.g., fine-structure eigenfunctions. The here presented new theory emphasizes the importance of nutation as an intrinsic energy bearing degree of freedom in spin-orbit coupling that has been overlooked in the past. The conclusions were made possible by rigorously solving the time-dependent one-electron Schroedinger equation in a reduced Hilbert space with spin- orbit and electric dipole interactions treated simultaneously. The energy expectation values of the resulting nonstationary precession states with nutation are shown to lye in a dynamical energy band limited by the stationary eigenvalues. Thus, this theory comprises the stationary eigenstates as precession states without nutation. As a precession state represents the most general state vector of an individual one-electron atom with spin- orbit interaction the same conclusions hold for mixed states representing statistical ensembles of such atoms.
Intracavity second harmonic generation in passively Q-switched Nd:YAG laser
Show abstract
Intracavity second harmonic generation of a passively Q- switched cw Nd:YAG laser is studied. The saturable absorber used was a Cr4+:YAG crystal, and the second harmonic generator was a flux grown KTP crystal. The results were compared to a case of acousto-optic Q-switched case. To allow for a unidirectional second harmonic output beam, a folded laser cavity was constructed. However, due to a partially transmitting mirror in the cavity, two output counter propagating second harmonic beams, were generated. Unexpectedly, 180 degrees out of phase periodic power variations of the two output beams were observed, as a function of the distance from the nonlinear crystal to the mirror.
Properties of light emission from silicon junctions
Show abstract
Some properties of radiation originating from an avalanching silicon light emitting diode (Si-LED) are dealt with. They are derived from various parts of the spectrum of the Si-LED light. The interdependence of the light output intensity (Li), wavelength ((lambda) ) and reverse current (IR) are determined, as well as the rate of change dLi/d(lambda) and dLi/dIR as a function of (lambda) and IR. The result demonstrate that Li and, to a much lesser extent (lambda) , can be controlled by IR.
Multiline Ti:sapphire laser by intrinsic birefringence
Andrei Ben-Amar Baranga,
Haim Lotem,
Ari Cohen
Show abstract
A multiline spectrum is imposed by intrinsic birefringence in the laser emission of a prism tuned Ti:Sapphire laser, pumped by flashlamp. With certain polarization alignments, the broadband obtained with a tuning prism in the hemispherical cavity is split into 10-20 equally spaced lines of less then 0.05 nm each. The effect, with potential multiline multiplexing applications, is crucial in laser alignment, with implications in Brewster cut crystal processing. The effect produced by the intrinsic birefringence in Ti:Sapphire crystal combined with the polarization introduced by the dispersion prism in the cavity, is explained and calculated for different experimental cases. For specific applications, one may design the multiline spectral separation and the total number of lines of a specific Ti:Sapphire laser. These parameters can be set to permit tunability over a certain range.
Holography, Micro-Optics, and Diffractive Optics
Multiple lenslet array imagers and correlators
Show abstract
An important factor in the success of electronic technology in the last few decades is the continuous drive for miniaturization: computing power that used to require a hall full of equipment fits nowadays comfortably in a notebook sized machine. The size of basic optical instruments, however, remained almost unchanged. Today, it is the size of optical devices and subsystems that limits further miniaturization of opto-electronic systems. Here, we describe and demonstrate optical configurations that enable us to design and fabricate very compact optical systems, based on the use of multiple micro-lens arrays. One such system is the multiple lenslet array imager (MLAI) that allows the distance between an object and its full size optical image to be as small as few centimeters, regardless of the size of the object. Another system is the lenslet array holographic correlator/convolver (LAHC), where we combine multiple lenslet arrays and a holographic filter to obtain a very compact optical correlator. Issues in micro-lens arrays fabrication and selected applications are discussed, and some laboratory demonstrations are presented.
Remote Sensing of Targets and Backgrounds
How do we search?
Joan F. Cartier,
David H. Hsu,
Jeffrey F. Nicoll
Show abstract
A target attractiveness model is used for field of view search. The model describes the search as a two-step process. The observer first decides to move to some location base don its attraction and size. These attractive points are further divided by a second decision which determines whether or not an observer will perform a detailed examination of the area or will choose a new attractive point. The model is tested on human performance experiments performed by the US Night Vision and Electronic Sensor Directorate.
Optical Materials
Field effect controlled photoconduction in PbS thin films
Lucian Pintilie,
Ioana Pintilie,
D. Petre,
et al.
Show abstract
A new structure is proposed for the PbS based photoresistors. This structure consists from a thin film of PbS (about 1 micrometer) chemically deposited on a dielectric layer (SiO2 or Si3N4 of about 2000 angstroms) grown, using different methods, on a single crystal Si wafer. The drain and the source contacts are the two gold electrodes evaporated on the surface of the PbS film. The resulting active area is of 6 by 6 mm2 and is subjected to an incident light with the wavelength in the domain 0.8 - 3 micrometer (at room temperature). The gate contact is the aluminum electrode evaporated on the back side of the Si substrate. Spectral distribution measurements were performed for different voltages applied on the gate electrode. It was found that the shape of the spectral distribution remains the same but the amplitude of the signal depends on the value and on the polarity of the applied voltage. An improvement of about 40% was obtained for the PbS photoconductive signal compared with the situation when the gate electrode is in air. The new structure offer the possibility to improve the photoconductive signal generated by the PbS film. This improvement is due to a field effect.
Lasers, Nonlinear Optics, and Quantum Electronics
Systems of fiber-coupled diode lasers as versatile sources of high-brightness radiation
L. Bartelt-Berger,
U. Becker,
Uwe Brauch,
et al.
Show abstract
Incoherent superpositioning of radiation from a single-mode fiber bundle with 200 mW output power per fiber allows to realize power densities of 2 MW/cm2. The total power being directly scalable with the number of fibers. With special optics for imaging the fiber-bundle endface onto the target instead of simply focusing it is possible to control the power density within that spot. Coherent superpositioning allows to further increase the power density and to direct the beam to a spot within the field of the incoherent superposition. Such systems could be useful for all kinds of applications requiring high-brightness radiation like cutting and welding or laser projection, printing plates, lithography, etc.
Remote Sensing of Targets and Backgrounds
Atmospheric scattering effect on spatial resolution of imaging systems: theory
Show abstract
The atmosphere is the optical medium between the imaging system and the observed object. The effect of this optical turbulent, absorbing and scattering element on the quality of an image is difficult to predict. Since the beginning of the sixties there were several attempts to build a model that will describe the degrading effect of the atmosphere on spatial resolution of imaging systems. In the field of atmospheric turbulence there is a common agreement on its relative contribution to the degradation of the spatial resolution of an image. On the other hand in the field of atmospheric scattering there is a disagreement on its degrading effects and an international scientific discussion has been developed in the past five years in this scientific field. A model, that was suggested several years ago by Sadot and Kopeika, claimed that the effect of the atmospheric scattering on the spatial resolution of imaging systems is a function of the properties of the imaging system, apart from the inherent properties of the atmosphere. The results of their model were in contrast with the results of the work of other scientists and therefore, caused a scientific debate. The purpose is to propose an alternative theoretical model which describes the effects of atmospheric scattering by focusing on the point spread function of the imaging system.
Atmospheric scattering effect on spatial resolution of imaging systems: experimental
Show abstract
This paper presents the results of a field experiment that was carried out in order to verify a physical model which describes the relationship between the optical properties of the atmosphere and the characteristics of an imaging system. The model depicts how different components of the light that are reaching the imaging system, after passing through the atmosphere, are detected by it. The measurements were done using a scanning point radiometer, while a local meteorological station measured the properties of the atmosphere. Theoretical predictions, which were achieved using a Monte-Carlo simulation of atmospheric scattering effects, are compared with the experimental data acquired in the field test. Comparison of theoretical predictions, using the above model, with the experimental data of other researchers is included. Both our data and the results of Luc Bissonnette of Canada supports the suggested model.
Holography, Micro-Optics, and Diffractive Optics
Infrared micromachined Fabry-Perot interferometer
Cazimir-Gabriel Bostan,
A. Corici,
S. Nan,
et al.
Show abstract
In this paper a Fabry-Perot interferometer fabricated by silicon surface micromachining is presented. The interferometer can be optimized for a wavelength of 1.3 micrometer, to act as an electro-mechanical modulator for fiber-optic network communications (fiber-in-the-loop applications), or for a range of wavelength from 1.5 - 7.5 micrometer, to act as a filter for IR spectroscopy in an IR gas analyzer.
Holographic studies of strain soliton evolution in nonlinearly elastic solid waveguides
Galina V. Dreiden,
A. V. Porubov,
Alexander M. Samsonov,
et al.
Show abstract
Results are presented from theory and experiments carried out to excite and observe a localized nonlinear longitudinal strain wave (soliton) in different waveguides. The wave parameters are calculated. It is shown that such a wave conserves its profile during propagation in an elastic waveguide.
Fiber Optics and Communications
Ultrafast tunable fiber-loop optical filters for dense WDM applications
Dan Sadot
Show abstract
A novel compact ultra-fast tunable fiber-loop filter is proposed. Although being implemented using currently available technologies, the filter tuning speeds are three orders of magnitude faster than other currently available filters - less than a nanosecond. The filter can be designed compact, and is immunized to external instabilities. By using compound configurations, multi-nanometer tuning range can be achieved, together with filer finesse of over 1000.
Industrial and Medical Applications
Angular dispersion of double-diffraction grazing-incidence spectrograph
Haim Lotem,
Mordechai Lando,
Avraham Lorber,
et al.
Show abstract
Utilization of linear array detectors in spectroscopy enables efficient and fast spectral data accumulation of entire spectral bands. The dependence of wavelength on the location along the detector is thus, a pertinent issue in modern spectroscopy. We discuss the behavior of the angular spectral dispersion of plane grating spectrographs in double- diffraction grazing-incidence geometry, and compare it to Littrow mounting. In the Littrow case, the dependence of the dispersion on wavelength is almost linear for narrow spectral bands, but the slope depends on wavelength. In contrast, in a double-diffraction grazing-incidence spectrograph the dispersion deviates strongly from linearity with wavelength. However, relative to the diffraction angle at a reference wavelength, (lambda) G, the shape of the dispersion curve in the band of maximum dispersion is, to a first approximation, constant and independent of the spectrograph wavelength setting. The reference wavelength is the one that is propagating normal to the plane folding mirror in the spectrograph, and it may be tuned by rotating the mirror. This characteristic of the dispersion is an important advantage in the calibrating process of the instrument.
Lasers, Nonlinear Optics, and Quantum Electronics
Solar-pumped solid state laser program
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Solar pumped lasers are candidates for wireless power transmission in space, free space optical communication and photochemistry. The present paper describes the progress on a joint project to develop solar pumped lasers, focusing on the temporal and spectral shaping of the laser beam, which comply with those applications. The program emphasizes the design, fabrication and testing of laser rods, passive and active Q-switches and non-linear crystals. This work is carried on in four projects, the first involves a study of possible applications of such a laser, which will determine the required solar pumped laser specifications. In the second project, the solar tower facilities at Weizmann Institute are used for studying the performance of the above mentioned laser components. The third project includes the construction of an innovative 7.5 kW solar concentrator at TEMED Industrial Park facility, to be used for the further study of laser components. The fourth project is dedicated to the development of a master oscillator-power amplifier chain, in which a diode-pumped laser serves as the initial oscillator, while the amplifier is solar pumped.
Holography, Micro-Optics, and Diffractive Optics
S-matrix propagation algorithm for full-vectorial electromagnetic simulation and design of gratings
Show abstract
S-matrix propagation algorithm for electromagnetic analysis of multilayer gratings with Rayleigh-Fourier implementation and TM-polarization issue renewal is overviewed. Examples of polarized-antireflection grating design are considered.
Optical Engineering
Beam delivery focusing objectives for excimer laser micromachining applications
Show abstract
Although the use of UV excimer lasers in photo-ablation and exposure applications is becoming more frequent, optical objectives for such applications are not widely available. In addition, high power UV excimer laser radiation limits the optical designer's choice of suitable materials and other design options when designing the beam delivery focusing objective. Now, however, a line of UV achromatic focusing objectives has been designed for photo-ablation applications. Thoroughly tested in the field, they are available as off-the- shelf standard components. Data are presented below on focal spot sizes, energy densities, and other focal characteristics for specific applications.
Industrial and Medical Applications
Operative dynamical tomography of optically transparent biological tissues
Michail M. Kugeiko
Show abstract
In the report the variant of the operative dynamical tomography is considered for the optically transparent biological tissues investigations based upon the linear moving of the emitting-receiving unit relative to the investigated tissue section. The radiation is sent and detected simultaneously at five directions (phi) i, specified by condition (phi) i equals arctan ((Delta) H)/i X (Delta) R, where i equals 1...5, (Delta) R and (Delta) H are spatial resolution at the tissue surface and penetration depth into the tissue, respectively. The interpretation of the obtained scattering signals is carried out at varying integration limit, corresponding to the emitting-receiving unit moving.
Angular dependence of sampling MTF
Show abstract
Sampling MTF defined in Park, Hock, and de Luca, as an x and y sampling, can be generalized for image data not along x and y directions. For a given sampling lattice (such as in a laser printer, a scene projector, or a focal plane array), we construct a two-dimensional sampling MTF based on the distance between nearest samples in each direction. Because the intersample distance depends on direction, the sampling MTF will be best in the directions of highest spatial sampling, and poorer in the directions of sparse sampling. We compare hexagonal and rectangular lattices in terms of their equivalent spatial frequency bandwidth. We filter images as demonstration of the angular-dependent two-dimensional sampling MTF.
Remote Sensing of Targets and Backgrounds
Imaging through the atmosphere from satellites: restoration of images based on atmospheric MTF
Show abstract
The recently developed atmospheric Wiener filter, which corrects for turbulence and aerosol blur and path radiance simultaneously, is implemented in digital restoration of AVHR imagery over the five wavelength bands of the satellite instrumentation. Restoration is most impressive for higher optical depth situations which cause more blur, with improvement in regard to both smallness of size of resolvable detail and contrast. Turbulence modulation transfer function (MTF) is calculated from meteorological data. Aerosol MTF is consistent with optical depth, measured with a sum-photometer. The product of the two yields atmospheric MTF which is implemented in the atmospheric Wiener filter. Turbulence blur, aerosol blur, and path radiance contrast loss are all corrected simultaneously, as if there were no intervening atmosphere. Image restorations with accompanying atmospheric MTF curves are presented. However, restoration results using a simple inverse atmospheric MTF filter were quite similar. This indicates the satellite images were characterized by very low noise and that turbulence jitter was very limited which, in turn, indicates that the turbulence MTFs integrated upwards over the path length wee not significant when compared to aerosol MTFs. Restorations are shown for various wavelength bands and are quite apparent even under clear weather conditions.
Fiber Optics and Communications
Design of an optical fiber amplifier with multiple serial pumping for space communications
Show abstract
The feasibility of an optical fiber amplifier as a booster amplifier for transmitter-terminals of free-space coherent laser communication systems has been investigated. To enhance the amplifier's efficiency and reliability in a harsh space environment a new pumping-scheme has been analyzed and demonstrated in an experimental set-up. The amplifier features efficient multiple serial coupling of the pump light into the multimode core of the double-clad fiber by using directional Y-couplers. Special attention has been paid to fiber-geometry, pump light absorption efficiency in the neodymium-doped single-mode core and the attenuation of pump and signal light.
Optical Engineering
Construction of a detection system with a wide field of view
T. Verker,
Naftali Schweitzer,
Jack Broder,
et al.
Show abstract
Filters used in communication systems in the atmosphere are usually of interference-filter type or of step-filter type. The major disadvantage of the interference filter is the limitation on the maximum incidence angle. In the step filter, the incidence angle is not limited. However, it has a wide spectral bandwidth. Therefore more background radiation enters the detector and as a result more noise is generated. The aim of this project is to design and fabricate an interference filter with a wide field of view. The filter is fabricated by evaporating thin films of suitable materials onto a transparent hollow hemisphere. The center of the detector will coincide with the center of the hemisphere. In this structure, the incident radiation always hits the filter at small angles independent of the transmitter position, so that the signal will always reach the detector.
Lasers, Nonlinear Optics, and Quantum Electronics
Performance of passive Q-switched, solar-pumped, high-power Nd:YAG lasers
Show abstract
Q-switched, solar-pumped, high power Nd:YAG lasers are attractive for a variety of applications requiring high instantaneous peak power density. The Q-switching can be obtained by an acousto-optic, electro-optic or passive device. Passive Q-switching seems an excellent choice for space as well as for other applications since it neither requires an external driver nor an electrical power supply. In recent years Cr+4:YAG single crystals were extensively used as passive Q-switches for flashlamp-pumped high power Nd:YAG lasers, demonstrating their superior thermal superior thermal characteristics and durability. In this work we report the first operation of passive Q- switched, solar-pumped, high power Nd:YAG lasers. The concentrated solar energy for he optical pumping of the laser was obtained by a 3-stage combination of imaging and non-imaging optics. It included: i) Weizmann Institute solar tower heliostats, ii) 3D compound parabolic concentrator, and iii) 2D compound parabolic concentrator in which the laser rod was placed. 72 mm long laser rods with either 3 mm or 4 mm diameter were used. The passive Q-switch was made from a Cr$=+4):YAG single crystal having a low- intensity transmission of 72 percent at 1.06 (mu) . Its rear surface was coated by a high reflectivity coating, serving as the rear mirror of the cavity. Output coupling mirrors with various reflectivities were used. The passive Q-switch demonstrated excellent durability and reliability during all the experiments. Repetition rates of 6-39 kHz were measured, showing higher repetition rates at higher laser power levels. The pulses demonstrated shorter full width at half maximum (FWHM) time for higher laser power elves, and the FWHM time range was 190-310 nsec. The maximal measured average power was 14 W. Thermal lensing was measured as a function of the absorbed solar power in the laser rod. It is estimated that laser peak power densities of approximately 100 kW/cm2 were achieved in the experiments. It is believed that near-future modifications may improve this value appreciably.
Remote Sensing of Targets and Backgrounds
Relation between thermal infrared and visible/near-infrared images of natural scenes: an overview
Show abstract
A Physical for the relation between reflective and thermal IR images of natural ground scenes is presented and discussed. The model enables the formulation of the joint distribution density function for the emitted radiance and its diurnal behavior. An approximated analytic expression for the multiband correlation coefficient is derived from the explicit form of the joint distribution function is calculated and presented. The effect of local scene topography and heat transfer mechanisms of vegetation on the obtained correlation coefficient is presented and analyzed. The main effect of the local scene topography is by introduction shaded areas which emit low radiance both in the thermal l and the reflective images. Vegetative objects regulate their temperature through evapotranspiration during daytime and hence usually becomes the coldest objects in the scene as their appearance in a visible image. Local scene topography effect can be estimated through a reasonable quantitative assessment of surface roughness characteristics and the relative geometry of the sun and the observation point. The resistance of vegetation to the external heat load is modeled via daytime and nighttime effective heat conduction. The effective heat conduction represents the unique heat transfer results which back the proposed model are presented. The model can be readily extended in order to describe the mutual relation between multispectral reflective images and thermal images. Furthermore, it enables us to interpret the effect of the addition of the thermal data on principal component analysis. The practical application of the model and its derived conclusions in the fields of remote sensing and data fusion are discussed.
Tracking point targets in cloud clutter
Show abstract
To realize the potential of modern staring IR technology as the basis for an improved IRST, one requires better algorithms for detecting unresolved targets moving at fractions of a pixel per frame time. While available algorithms for such targets in white noise are reasonably good, they have high false alarm rates in non-stationary clutter, such as evolving clouds. We review here a new class of temporal filters which have outstanding signal to clutter gains in evolving clouds and still retain good signal to temporal noise sensitivity in blue sky or night data. The generic temporal filter is a damped sinusoid, implemented recursively. Our final algorithm, a triple temporal filter (TTF) based on six parameters, consists of a sequence of two damped sinusoids followed by an exponential averaging filter, with an edge suppression feature. Initial tests of the TTF filter concept demonstrated excellent performance in evolving cloud scenes. Three 'trackers' based on the TTF operate in real-time hardware on laboratory IR cameras including: an empirical initial version; and tow recent forms identified by an optimization routine. The latter two operate best in the two distinct realms: one for evolving cloud clutter, the other for temporal nose-dominated scenes such as blue sky or stagnant clouds. Results are presented both as specific examples and metric plots over an extensive database of local scenes with targets of opportunity.
Optical Materials
Refractive and diffractive micro-optical elements and arrays prepared by the fast sol-gel processes
Yair Haruvy,
Irith Gilath,
M. Maniewictz,
et al.
Show abstract
The optical quality of films and bulk elements obtained by the fast sol-gel method and the ease of preparation make this method technologically and economically attractive for micro- optical elements and arrays. Multiple replication of high-cost metal templates necessitates a two step process: initial replication onto disposable plastic, to produce negative- templates, and casting of the glass elements onto these plastic templates. Following introduction of the fast sol-gel micro-replication processes, the fabrication of refractive and diffractive micro-optical arrays is described in detail. The study focuses of the accuracy achievable by the replication of sharp curvatures by a viscous sol-gel resins. A further question addressed is how to obtain a thick crack-free self- supporting micro-optical array by such a process. Examples of replication results of Fresnel lenses and various types of lenslet arrays by this method are shown, and the various aspects of replication accuracy are discussed. The characterization of the thus produced micro-optical arrays is described, relating to the influence of mold and resin parameters on residual stresses and thence, the surface and bulk properties of the replicas. Various approaches to stress- minimization that can facilitate accurate replication in sol- gel derived matrices are discussed. Further, the preparative approach to highly patterned crack-free self-supporting thick elements is displayed, and the wide scope of new applications stemming from such elements is discussed. Finally, the new chemical approach to crack-free stress-free silica glasses by the sol-gel method is displayed.
Remote Sensing of Targets and Backgrounds
Image restoration for target detection: will it help?
Show abstract
The classical method for determining target acquisition probabilities has always focused on the maximum spatial frequency (frmax) discernible in the image. On the other hand, it is known that the atmosphere degrades all the spatial frequencies as determined by the atmospheric modulation transfer function (MTF). The question arises: do the 'other' frequencies below frmax affect the target acquisition probability. We will present two experimental approaches to this question. In the first, we consider different atmospheric MTFs with the same value of frmax but with different MTF shapes. In the second, we consider a novel Wiener filter which restores all the frequencies to their value prior to the atmospheric blur. Laboratory measurements of observer response time when performing target acquisition will be presented for these case. The results will allow us to check the degree that the entire MTF should enter the target acquisition model, rather than frmax only.
Lasers, Nonlinear Optics, and Quantum Electronics
One-dimensional and two-dimensional spectral interference measurements of ultrashort optical pulses
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1D and 2D linear spectral interference measurements of ultrashort pulses are shown. The methods involve measurements of the spectral interference pattern between ultrashort reference and signal pulses, from which the spectral phase difference can be extracted. 1D measurements require post-processing to extract the phase. 2D measurements require no post-processing, and are therefore most suitable for visual interpretation. Dispersion of optical glasses, as well as crafted spectral phase discontinuities are measured. The methods are applicable to single shot measurements of extremely weak pulses.
Third harmonic generation for nonlinear scanning laser microscopy
Show abstract
Third harmonic generation near the focal point of a tightly focused beam is used to probe microscopical structures of transparent samples. The axial resolution at which this method can resolve interfaces and inhomogeneities is shown to be comparable with the confocal length of the beam. Using 125 femtosecond pulses at 1.5 micrometers , we were able to resolve interfaces with a resolution of 1.2 micrometers and to produce 2D cross-sectional images of the samples used.
Optical Materials
Method of optical enhancement during the exposure process on thin films of vitreous chalcogenide semiconductors
Show abstract
A method for the storage of information on vitreous chalcogenide semiconductor (VCS) thin films by timing exposures so as to produce photoinduced changes (PIC) in the VCS layers, was published at an earlier date. This paper refers to an interesting phenomenon observed during holographic recording on VCS induced by the homogeneous light produced by a HE-Ne laser, for hologram control or reconstruction. This effect can be regarded as self- enhancement, as the holographic image is enhanced during its reconstruction. The exposures that are greater than Hmax, at first decrease the self-enhancement effect and can even erase the optically recorded data. The speed of optical erasure tends to increase for longer exposures. However, this very effect of erasure of holograms recorded on VCS layers may be used as a basis of reconstruction, provided the PIC was made by lasers of sufficient power.
Halftone imaging on photothermoplastic media by interference prerastering
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This paper refers to the study of processes conducting to halftone image recording on photothermoplastic media (PTPM) by the preliminary formation of raster surface gratings. Whenever a pre-rastering recording method is used, it has two charging cycles which include: (1) Preliminary formation of raster grating by recording an interference grating on the PTPM surface; (2) Partial non-charging thermal erasure of the raster grating by continuous PTPM heating; (3) Examination of the photographic characteristics of rastered gray-scale images during recording by a second charging of PTPM. The methodology employed provides the necessary diffraction efficiency (DE) in the illuminated areas of the PTPM as well as a low DE value in background areas, so as to achieve a maximum PTPM photosensibility of up to S equals 106 cm2/J, and a contrast coefficient (gamma) equals 1.4, while the maximum contrast value of recorded images is Km greater than 40.
Industrial and Medical Applications
Noncontact testing of optical surfaces by multiple-wavelength light scattering measurement
Show abstract
An instrument is described which enables the detection of backscattered light within a wide spectral region. The apparatus is based on a Coblentz sphere and is equipped with light sources from the UV to IR spectral region (248 nm to 10.6 micrometer). Results are reported of measurements on samples with different surface qualities such as supersmooth Si-wafers with sub-angstrom surface roughness, glass substrates, thin film optical components and machined surfaces. The set-up complies with a corresponding ISO project.
Fiber Optics and Communications
Fiber optic microphone as a realization of fiber optic positioning sensors
Alexander Paritsky,
Alexander Kots
Show abstract
A new fiber optic method to measure distances possesses very high distance resolution and may be used to construct different kind of sensors. As an example of it possibilities an example of unique construction of super small and super sensitive fiber optic microphone is demonstrated.
Holography, Micro-Optics, and Diffractive Optics
Visual tool for electromagnetic simulation and design of multilayer grating structures
Show abstract
A visual tool for optical properties (reflection and transmission) simulation and design of multilayer lamillar grating structures is developed, and reported in this work. The simulations are based on rigorous electromagnetic analyses using S-matrix propagation algorithms which are implemented with Fourier-transform discretization, and are coded in Matlab. Visual C++ software tools are used to feed in the input parameters and feed out the results. The input parameters include: input structure, optical and materials parameters. The tools run on a pc. Examples of some of the screen frames obtained by the tools are presented.
Lasers, Nonlinear Optics, and Quantum Electronics
Intensity and interferometric autocorrelation measurements of ultrashort pulses by third harmonic generation
Show abstract
Intensity and interferometric autocorrelation measurements of femtosecond pulses by third harmonic generation are demonstrated. The third harmonic signal is generated by tight focusing of the femtosecond pulses on the surface of an ordinary glass slide, which serves as the nonlinear medium. The method is shown to be applicable to real-time measurements.
Industrial and Medical Applications
Detection of cancer by means of infrared spectroscopy
Show abstract
We have measured the mid-infrared spectra of several tissues in a malignant and normal state, using the ATR sampling method. The aim of the experiments was to detect cancer signatures that were discovered earlier using other sampling methods. The ATR method is particularly attractive for medical applications because it can be used in-vivo, and because it requires minimal sample preparation. We have succeeded to detect a significant signature in only one of the five spectral bands that were examined. This signature is attributed to the PO2- symmetric stretching of the nucleic acids phosphodiester groups, and is located in the vicinity of 1082 cm-1. The signature consists of a shift in the maximum absorption peak by 3 cm-1. The measured data is in good agreement with the published data. This result can lead to real-time tumor mapping during surgery and in-vivo cancer diagnosis with fiber-optic ATR probes.
Optical Materials
Influence of substrate surface and film roughness on the quality of optical coatings for the UV spectral region
Show abstract
Effects of defect propagation from the substrate throughout thin film single layer and multilayer coatings are investigated on fluoride and oxide films evaporated onto different types of substrates. Atomic force microscopy, light scattering methods, and transmission electron microscopy are used to study the surface morphology of the coated and uncoated substrates. With fluoride films, propagation of rough substrate structures is observed for both single layer films and multilayers. Oxide coatings replicate the microtopography even of well polished surfaces and throughout thick multilayer stacks.
Lasers, Nonlinear Optics, and Quantum Electronics
Lasing without cavity
Show abstract
Optical gain media filled with strong scatterers present a laser-like emission when optically pumped.Different regimes can be evidenced where amplified spontaneous emission together with multiple scattering play the main role. A mapping technique where both the concentrations of dye molecules and scatterers are independently varied allows to differentiate between those regimes. A simple model based on photon diffusion is presented and threshold for lasing emission is derived, and is compared with the experiment. Qualitative agreement is found, showing that the threshold critically depends on the samples macroscopic size.
Fast energy transfer between subsites in wide-bandgap luminescent materials
Show abstract
When analyzing energy transfer between donors and acceptors in solid-state materials, anomalous energy transfer may occur. When it does, the effect may not be apparent in the donor day; however, the effect in the acceptor excited-state concentration can be drastic. Examples are given from actual multi-site decays.
Holography, Micro-Optics, and Diffractive Optics
Sol-gel prepared glass for micro-optical elements and arrays
Yair Haruvy,
Irith Gilath,
M. Maniewictz,
et al.
Show abstract
Sol-gel processes of metal alkoxides involve hydrolysis of the alkoxy groups and condensation to a 3-D oxide glass network. Volume reduction of the drying gel typically results in cracking, unless sufficient relaxation is allowed to take place. Further, the common shrinkage by a factor of 2.5 and higher imposes great difficulty to obtain dimensional accuracy in thus prepared micro-optical elements. The new fast sol-gel method enables facile preparation of siloxane-based glassy materials in which polymerization is completed within minutes and curing within a few hours. The optical quality of thin films obtained by the fast sol-gel method and the ease of preparation makes this method technologically and economically attractive for micro-lenses and micro-optical arrays by replication. Micro-optical arrays are highly patterned, including sharp curvatures of small radii. This necessitates to study primarily two aspects of the sol-gel replication process: (1) the chemical constitution of the sol-gel and the reaction pathway that ensures prompt adhesion to the template during the process. (2) the surface chemical adaptation of the template that allows timing of adhesion and release of the produced elements. The adaptation of this process to the desired replication is described. Thence, the results of preliminary fabrication of micro-optical elements and arrays by this method are shown and their features discussed.
Remote Sensing of Targets and Backgrounds
Optical similarity of turbulent jets
Show abstract
Similarity of radiation characteristics of heated turbulent jets was revealed experimentally and confirmed theoretically. A universal function that describes thermal radiation of many jets with different outlet parameters was found. A method was developed for prediction of IR radiation emitted by exhaust jets in finite spectral intervals containing many spectral lines.
Dual-mode spectral detection of hypersonic flows
Deborah A. Levin,
Leonard H. Caveny,
Guy W. Beaghler,
et al.
Show abstract
In this paper the elements of supporting research required to analyze the key components of a dual-mode interceptor- borne seeker are discussed. The sensor window background radiation in the MWIR and UV are presented. Images of a plume, a likely target source, in the UV and MWIR are also presented.
Lasers, Nonlinear Optics, and Quantum Electronics
Cubic domains in tetragonal ZnGeP2 single crystals
Show abstract
ZnGeP2 crystallizes congruently through an (beta) > (alpha phase transition. The high temperature (beta) -phase has a diamond-like cubic structure, with Zn and Ge ions randomly distributed on the metal sublattice. The (alpha) - ZnGeP2 crystal has an ordered tetragonal structure, in which the Zn and Ge ions occupy different crystallographic sites. In the present study, good quality ZnGeP2 crystals have been grown by means of the Horizontal Gradient Freezing technique. A small amount of coherently oriented domains of the cubic (beta) -ZnGeP2 structure was identified, however, within the tetragonal ZnGeP2 crystals, indicating an incomplete transition. The (beta) - ZnGeP2 phase was partially retained by rapid quenching from the melt.
Generation of partially coherent fields with twist
Show abstract
It is shown, theoretically and experimentally that any astigmatic beam with M2>1, coherent or partially coherent, can be transformed by a first order system into a beam with second intensity moments of circular symmetry and twist. Experiments were performed with coherent Gauss- Hermite beams of high order and partially coherent diode arrays. Furthermore it is demonstrated that the bema parameter product is not constant in ideal ABCD-system.
Holography, Micro-Optics, and Diffractive Optics
New computer-generated hologram
Show abstract
A method for calculating in real time, the transmission function of a computer generated hologram (CGH) for beam shaping, is described. This method is based on the well known phase contrast method (PCM) in which phase distributions of an object are transformed to intensity distributions. In the phase contrast-like system a desired intensity distribution is obtained by using a special phase mask.
Optical Materials
New performance of n-type InSb photoconductive detectors
Show abstract
This paper reports on the new performance obtained for n-type InSb photoconductive element detectors, made of bulk crystals. It is taken into account the important drop of the electric conductivity, by one magnitude order over the temperature range 77 K - 90 K, that forced us to optimize the heat transfer among the elements of the device. The maximum value obtained for the spectral detectivity is 4 by 1012 cmHz1/2W-1, at lambda equals 4.9 micrometer, for a field of view of 60 degrees. The calculations show that the device is limited by the generation-recombination noise.
Remote Sensing of Targets and Backgrounds
Prediction of heated jet radiation with account of turbulent fluctuations
Show abstract
The results of the investigations of turbulent fluctuation influence on heat radiation of hydrocarbon fuel combustion jets are presented. These results show that temperature fluctuations are one of the basic factors forming radiation fields on non-reactive jets. The approach used is based on optically thin pulsation approximation that allow to account for temperature fluctuation contribution using local averaging of optical characteristics in radiation transfer equation. Such averaging may be completed using model probability density functions (PDF) of temperature and concentration. Several PDF models were verified on the basis of measured and calculated jet IR radiance comparison.
Optical and Image Processing
Evaluation of the PSF from motion-blurred images
Show abstract
This paper deals with the problem of restoration of images blurred by relative motion between the camera and the object of interest. This problem is common when the imaging system is in moving vehicles or held by human hands, and in robot vision. For correct restoration of the degraded image we need to know the point spread function (PSF) of the blurring system. In this paper we propose a method to identify important parameters with which to characterize the PSF of the blur, given only the blurred image itself. The identification method here is based on the concept that image characteristics along the direction of motion are different than the characteristics in other directions. Depending on the PSF shape, the homogeneity and the smoothness of the blurred image in the motion direction are higher than in other directions. By filtering the blurred image we emphasize the PSF characteristics at the expense of the image characteristics. The method proposed here identifies the direction and the extent of the PSF of the blur and finally identifies the modulation transfer function (MTF) of the blurring system.
Lasers, Nonlinear Optics, and Quantum Electronics
Tunable intracavity RbTiOAsO4 OPO in the mid-IR
Show abstract
An RTA intracavity OPO was demonstrated in a diode side- pumped Nd:YAG, Q-switched, hemispherical oscillator. Tuning range of 3.0 to 4.1 micrometers was achieved. Total conversion efficiency from diode light to idler was 0.5 percent.
Optical and Image Processing
Vibrated image restoration from two consecutive images
Show abstract
Vibrations are often a major cause of image degradation in airborne ad terrestrial reconnaissance, astronomy, robotics, machine vision and computer vision systems. In the case of low-frequency vibration (the exposure time is shorter than the vibration period time) the camera motion during the exposure is random, depending on the vibration parameters (amplitude and frequency) and on the instant of the exposure time. Therefore, the random motion causes a random image blur. Knowledge of the exact motion is practical for calculation of motion optical transfer function (OTF) which can be used with common image restoration algorithms. The motion can be either measured directly using motion sensors or estimated from a sequence of images. Here, a vibration motion estimation method from a minimal sequence of two images is presented. Motion estimation from only two consecutive images is possible due to the use of information hidden in the image blur. The process is carried out in the frequency domain using a new analytical motion OTF calculation method.
Lasers, Nonlinear Optics, and Quantum Electronics
Faraday rotators for use in multijoule Nd:Cr:GSGG and Nd:glass phase and polarization conjugated multiple-pass amplifiers
Show abstract
High fluence solid-state lasers were built using Nd:Cr:GSGG or Nd:glass in oscillator/multiple-pass phase and polarization conjugated amplifier configurations. Beam path control, thermal stress induced birefringence correction, and isolation were achieved using Faraday rotators. Damage threshold on material and on pulse duration were investigated. Terbium glass was found to have a damage threshold five times greater than that of TGG. The damage threshold of both Terbium doped materials was virtually independent of pulse duration.
Fiber Optics and Communications
Performance limitations of free-space optical communication satellite networks due to vibrations: direct-detection digital mode
Show abstract
Free space optical communication between satellites networked together can permit high data rates between different places on earth. The use of optical radiation as a carrier between the satellites permits very narrow beam divergence angles. Due to the narrow beam divergence angle and the large distance between the satellites the pointing from one satellite to another is complicated. The pointing task is further complicated due to vibration of the pointing system caused by tracking noise and mechanical impacts. In this work we derive mathematical performance models for digital direct detection communication satellite networks as a function of the system parameters, the number of satellites, and the vibration amplitude. The optical inter- satellite network model considered includes a transmitter satellite, regenerative satellites, and a receiver satellite all networked together. A comparison between three communication system modulation schemes on-off keying, pulse position modulation, and pulse polarization binary modulation is presented. These models are the basis for optical communication tracking and pointing system design of appropriate complexity and performance in order to make the network as simple and inexpensive as possible. From the analysis it is clear that even low vibration amplitude of one satellite pointing system decreases dramatically the network performance.
Remote Sensing of Targets and Backgrounds
Novel applications of hyperstereo vision
Show abstract
Recent stereo vision experiments show potential in enhancing vehicular navigation, target acquisition, and optical turbulence mitigation. The experiments involved the use of stereo vision headsets connected to visible and 8-12 micrometers IR imagers. The imagers were separated by up to 50 m and equipped with telescopes for viewing at ranges of tens of meters up to 4 km. The important findings were: (1) human viewers were able to discern terrain undulations for obstacle avoidance, (2) human viewers were able to detect depth features within the scenes that enhanced the target acquisition process over using monocular viewing,and (3) human viewers noted appreciable reduction in the distortion effects of optical turbulence over that observed through a single monocular channel. For navigation, stereo goggles were developed for headset display and simultaneous direct vision for vehicular navigation enhancement. For detection, the depth cues can be used to detect even salient target features. For optical turbulence, the human mechanisms of fusing two views into a single perceived scene can be used to provide nearly undistorted perception. These experiments show significant improvement for many applications.
Optical and Image Processing
CCD camera baseline calibration and its effects on imaging processing and laser beam analysis
Show abstract
CCD cameras are commonly used for many imaging applications, as well as in optical instrumentation applications. These cameras have many excellent characteristics for both scene imaging and laser beam analysis. However, CCD cameras have two characteristics that limit their potential performance. The first limiting factor is the baseline drift of the camera. If the baseline drifts below the digitizer zero, data in the background is lost, and is uncorrectable. If the baseline drifts above the digitizer zero, than a false background is introduced into the scene. This false background is partially correctable by taking a background frame with no input image, and then subtracting that from each imaged frame. ('Partially correctable' is explained in detail later.) The second characteristic that inhibits CCD cameras is their high level of random noise. A typical CCD camera used with an 8-bit digitizer yielding 256 counts, has 2 to 6 counts of random noise in the baseline. The noise is typically Gaussian, and goes both positive and negative about a mean or average baseline level. When normal baseline subtraction occurs, the negative noise components are truncated, leaving only the positive components. These lost negative noise components can distort measurements that rely on low intensity background. Situations exist in which the baseline offset and lost negative noise components are very significant. For example, in image processing, when attempting to distinguish data with a very low contrast between objects, the contrast is compromised by the loss of the negative noise. Secondly the measurement of laser beam widths requires analysis of very low intensity signals far out into the wings of the beam. The intensity is low, but the area is large, and so even small distortion can create significant errors in measuring beam width. The effect of baseline error is particularly significant on the measurement of a laser beam width. This measurement is very important because it gives the size of the beam at the measurement point, it is used in laser divergence measurement, and it is critical for realistic measurement of M2, the ultimate criterion for the quality of a laser beam. One measurement of laser beam width, called second moment, or D4(sigma) , which is the ISO definition of a true laser beam width, is especially sensitive to noise in the baseline. The D4(sigma) measurement method integrates all signals far out into the wings of the beam, and gives particular weight to the noise and signal in the wings. It is impossible to make this measurement without the negative noise components, and without other special algorithms to limit the effect of noise in the wings.
Development of a database filter based on optoelectronic smart pixel arrays
Show abstract
We presented here the design and initial demonstration of three optoelectronic database filters. Each of these systems is intended to serve as an interface between a page oriented optical storage devices and an electronic host computer. In addition to providing optical/electrical data conversion, each filter is capable of reducing the high data rate optical input to low data rate electronic signals compatible with conventional database management systems. For each filter, the system objectives and associated design trade offs are presented. Finally, an overall trend towards increasing pixel logic complexity while reducing optical system complexity is discussed.
Wavelet image processing for optical pattern recognition and feature extraction
Show abstract
This paper discusses a new method for performing wavelet-based pattern recognition and feature extraction. Known as 'progressive pattern recognition,' this approach is based on performing a subband transform of a target image and then performing partial correlations with different subband resolutions; it is possible to recognize the image without correlating against the complete wavelet transform, thereby realizing considerable savings in computational time. Computer simulations of palm print recognition are presented, and extensions to both scale and rotation invariant systems and optical implementations are discussed.
Remote Sensing of Targets and Backgrounds
Space-based small ultraviolet photometer for the measurement of ozone concentration in the Earth's atmosphere
Show abstract
The Ozone Meter (OM-2) described in this paper is designed to obtain both ozone profiles and cumulative ozone amount in the earth atmosphere from space measurements of solar backscatter ultraviolet radiation. OM-2 uses a filterwheel- photometer combination to measure UV radiation in the 252.0- 340.0 nm spectral region in 7 fixed wavelengths with 1.0 nm bandwidth. This short form report describes the OM-2 according to its optical scheme, detector, electronic parts, the filter wheel mechanism, the filters and the mechanical design. This technique can detect large variations of ozone a broad range of atmosphere with errors ranging up to 15 percent. The OM-2 instrument has small weight and size, low power consumption and an accuracy similar to that of more complicated instruments used in the past. The OM-2 will be a part of the instrument pack of the Israel microsatellite TechSat-1A that will be launched in 1997.
Optical Materials
Laser-induced chemical vapor deposition of optical thin films on curved surfaces
Shoshana Tamir,
S. Berger,
Kopel Rabinovitch,
et al.
Show abstract
Laser induced chemical vapor deposition (LCVD) of silicon nitride and silicon dioxide single and double layers have been investigated using excimer laser operating at a wavelength of 193 nm. The composition of silicon nitride which was formed in SiH4/NH3 gas mixture was nearly stochiometric having a refractive index of 1.8 - 1.9 and contained small amount of hydrogen. Deposition of silicon dioxide was investigated using SiH4/N2O. Using this gas mixture the film composition depended strongly upon the SiH4/N2O ratio. At high ratio the film formed was silicon oxynitride, which contained both Si-N and Si-O bonds. The film also contained small amount of Si-H bonds. Decreasing SiH4/N2O ratio led to the formalin of pure silicon dioxide with a refractive index of 1.45. A double layer coating of both silicon nitride and silicon dioxide resulted in the formation of antireflection coating with a reflectivity of about 0.5% at 750 nm.
Industrial and Medical Applications
Comprehensive optical diagnostics of complex flow fields
Show abstract
This paper describes a series of promising optical diagnostic techniques to provide a comprehensive acquisition of the optical information from various flow fields under investigation. A simultaneous application of the two or even several diagnostic techniques which combines a CFD code calculations yield more accurate measurements of the density and/or the density gradient distributions in complex flow fields. Traditionally qualitative data of the density gradient in a high speed compressible flow have been obtained by schlierengraphy. A white light source and a laser two optical arms schlieren optical schemes were constructed on the base of a conventional schlieren system. The optical image of a model was focused on a photo film and projected on a screen. A CCD- camera was used to catch the focused image in real time, to display it on a control monitor and to record it on a video tape recorder. An acoustically stable holographic variable shear interferometer, which has been easily constructed on the base of the conventional schlieren system allowed to record a signal hologram during the wind tunnel run by using a continuous wave laser light source. Signal and comparison holograms have then been post-processed by the dual hologram technique to display shearing interferograms. A holographic Moire deflectometry method is presented. The holographic recording provides a 'freezing' of the distorted signal wave on a hologram to analyze it a posteriori by the Moire technique. A novel holographic Moire interferometer is described and its application to testing a small size axisymmetric supersonic air jet is shown. An interference method with enhanced sensitivity and compensating for optical aberrations, which is based on rerecording holograms is briefly described. It would provide a reliable acquisition of the phase information from wide range of weak phase objects including high speed low density flow fields. The method has been demonstrated by mapping the density field of the supersonic air jet as a representative weak phase object. The numerical analysis of a 2-D flow field was also carried out by means of computational fluid dynamics (CFD) methods.
Remote Sensing of Targets and Backgrounds
Automatic detection of targets using hierarchical spatial/temporal processing
Eliezer Haber,
Yehuda Sylman
Show abstract
An algorithm for automatic target detection has been developed.An image is processed using a pyramidal structure in a two stage process. Each frame is spatially filtered to identify potential target areas. The temporal behavior of blobs identified is analyzed; targets are declared where blobs exhibit motion consistent with targets of interest. Targets of different sizes are detected at different pyramid levels. A single target will usually be detected at several levels. Integration of information from the various levels is essential. Two data merging approaches were examined. The first projects blobs from each level to the pyramid base. Blobs exhibiting target-like behavior are extracted. The second innovative approach builds tracks on each level. Only blobs jointed to tracks are projected to the base. Tracks are formed on these projections. Targets are declared on tracks that achieve a given quality. This hierarchical approach permits the system to operate with great sensitivity. False detections are eliminated at two stages. Most spurious blobs will not form tracks at the pyramid levels and will not be projected to the base. Tracking at the base eliminates others. Experimental results demonstrate high detection probability and low false alarm rate under a wide variety of conditions.
Holography, Micro-Optics, and Diffractive Optics
Analytical design of a focusing double grating coupler (FDGC)
Gil Mildworth,
Yaakov Amitai
Show abstract
In this paper, we present a method to design a focusing double grating coupler (FDGC), which couples a polychromatic wave out of a waveguide and focuses it with only a negligible angular dispersion. The aim of the design is to construct two grating functions in such a way that the chromatic dispersions of the two gratings will compensate each other mutually. To achieve that, we use an iterative method, where the main idea is to design a double grating which deflects and focuses with no dispersion two different wavelengths resulting in negligible dispersion inside the band. The FDGC described in this paper can be applicable to many devices. In particular, the FDGC provides an attractive solution to be used in various applications of integrated optics, as well as in optical parallel computing. In addition, it can be implemented within a wide variety of applications such as a CD player, optical mass storage devices or any other application that incorporates a solid state laser and a focusing lens.
Designing a thermal imaging system with hybrid diffractive-refractive lenses
Yoel Blumenfeld,
Yaakov Amitai
Show abstract
A new design of a thermal imaging system which incorporates diffractive surfaces in order to enhance system performance is presented. The problem of the drastic vignetting, typical of Galilean telescopes, is solved by using a Keplerian telescope with a very small f-number (approximately 0.7). In addition, several other aspects of design, manufacturing and tolerancing are discussed.
Planar diffractive elements as Bragg volume holograms versus surface relief gratings
Show abstract
A method for designing and fabricating optical systems based on planar holographic optics is presented. The planar optical system is usually composed of two (or more) holographic optical elements which are fabricated onto the same substrate. This paper compares and contrasts the two principal fabrication methods of holographic elements as Bragg volume holograms or as surface relief gratings. Various examples of planar holographic optical systems are presented, and their advantages over regular optical systems are illustrated.
Optical and Image Processing
First-order analysis of thermal defocus in infrared imaging systems
Jonathan B. Cohen
Show abstract
Thermally induced defocusing exists in all optical systems, but is a particularly acute problem in imaging systems for the mid- to far-infrared. This is due to the fact that there are a limited number of optical materials for this spectral range, which are generally highly sensitive to changes in temperature. Most infrared imaging systems fall into two broad categories: scanned systems with a line detector, and staring- array systems. Each of these has components with fairly well- defined paraxial characteristics, so that the first-order data of the system as a whole is amenable to analysis during the preliminary stages of optical system design. For each of the various component sub-systems, the thermal variation of focal length can be calculated for any of several configurations (e.g. achromatic doublet, or diffractive element), based on the coefficients of thermal expansion and of thermal variation in refractive index of the optical materials. By combining the thermal characteristics of the optical sub-systems with the first-order optical characteristics, one obtains a first-order analysis of the optical system's thermal characteristics, including the rate of thermal defocus, and the range required for a particular thermal defocus adjustment.
Fiber Optics and Communications
Mode coupling coefficient in chalcogenide-glass multimode fibers in the midinfrared
Show abstract
The optical power distribution along step index As2Se3 chalcogenide-glass multimode fibers in the mid IR region was studied experimentally. The experimental set-up consists of an Ir source with collimating and focusing optics, and step index As2Se3 multimode fibers in different lengths. The far field radiation intensity of the fiber was obtained by moving an MCT detector with different band pass filters on an arc centered at the fiber exit.
Acousto-optic interaction in two-mode optical fibers
Kjell Blotekjaer,
Helge E. Engan
Show abstract
Optical and acoustic properties of two-mode optical fibers are described. The principle of acousto-optic interaction between the LP01 and LP11 modes is explained, and typical experimental setups are described. Experimental results for frequency shifters, tunable filters, and scanning interferometers base on two-mode acousto-optic interaction are presented. The importance of fiber nonuniformity is discussed.
Remote Sensing of Targets and Backgrounds
Remote sensing of atmosphere and water media under conditions of a priori uncertainty
Michail M. Kugeiko,
Dmitry M. Onoshko
Show abstract
The greatest difficulties at the determination of optical characteristics occur at the remote sensing of complex scattering media under conditions of absence of a prior information about medium under investigation. Such media correspond to the atmosphere of large industrial towns. Known one-frequency methods of interpretation of lidar measurements results have low accuracy of the determination of optical characteristics profiles and, the more so, as microphysical characteristics profiles because of considerable discrepancy between the real media and their model representations, for which the processing algorithms have been obtained. Moreover, the additional independent measurement are required in order to determine base values or attenuation coefficients in the certain points on the sensing route, or the transparency of the route interval. This requirement significantly reduce the operational advantages of the remote lidar method. The mentioned flaws are remedied in the proposed here processing technique of the lidar measurements data.
Optical Engineering
Conjugated cavity with a wide field of vision
A. F. Kornev,
V. P. Pokrovsky,
V. K. Stupnikov,
et al.
Show abstract
Methods of optical design, numerical simulation and experimental testing results are given for the super wide field of vision conjugated optical resonator.
Holography, Micro-Optics, and Diffractive Optics
Numerical simulation of observational telescope with the dynamic holographic correction
Nataly A. Bezina,
Alexey Leshchev,
Michael V. Vasil'ev,
et al.
Show abstract
Described are the methods of numerical design and simulation of observational telescopes, using the thin (plain) dynamic hologram as the corrector for image distortions, imposed by the primary mirror surface defects.
Optical Engineering
Radiometric calibration for InSb FPA camera
Show abstract
Novel methods for radiometric calibration of InSb FPA camera were developed and tested. An advanced weighting function method is used in order to transform a pixel gray level (14 bit digitized and corrected by the nonuniformity correction -- NUC electronics) into the integral radiance (over the camera spectral bandwidth) on the target plane. The study can be applied for various InSb FPA cameras with controlled integration times, high stability of their NUC-electronics and large dynamic range of its data acquisition board.
Lasers, Nonlinear Optics, and Quantum Electronics
Measuring dynamic chirp in DFB lasers using an all-fiber implementation
Show abstract
The temporal response of the optical frequency of a single- frequency DFB laser under direct current modulation is an important parameter for evaluating the performance of optical communication systems. Using an all-fiber Mach- Zehnder interferometer, serving as a frequency discriminator, this temporal response was measured with time resolution of 0.1nS and frequency resolution of 100MHz. While similar schemes were previously built for the same purpose, this is the first all-fiber implementation that uses no moving parts. This setup was successfully used to measure and model the adiabatic and thermal chirp of a 1.3 micrometers DFB laser. The same setup as also used for direct measurements of the laser's FM response.
Optical Materials
UV devices for solar blind and background limited detection
Show abstract
A technology has been developed for producing polymer based UV absorption filters. The filters are fabricated by embedding UV absorbing dyes in polymer matrices. A selection of dyes with different chromophores have been synthesized. Each provides a high level of blocking within a specific band in the UV. Polymer filters are combined with other filtering components that absorb in the visible and IR regions to form selective UV bandpass filters. Typical filter combinations achieve transmission levels of 10% and more in the mid UV and absorption levels reaching up to 12 OD and higher in the remaining UV, visible and near IR regions. An important advantage of these UV bandpass filters is the exclusive use of absorption type components. This provides consistent performance over wide acceptance angles. Filters with spectral transmission profiles optimized for specific detection applications in the UVc and UVb regions have been designed. Optimization takes into consideration the spectral response of the detector to achieve the sensor spectral response required by the application. Solar blind PMT sensors incorporating these files have demonstrated blindness to noontime solar illumination while maintaining good response from 245 to 270 nm in the solar blind range. Complete blocking of solar radiation and good sensitivity in the solar blind range has also been achieved with SiC solid state photodiodes.
Fiber Optics and Communications
Wavelength dependence of the principal states of polarization in short segments of doped fiber
Show abstract
Due to various imperfections, such as core ellipticity, as well as internal and external stresses, single mode fibers are birefringent. In general, the magnitude and orientation of the birefringence varies randomly along the fiber. This leads to the well known phenomena of polarization mode dispersion in fiber-optic communication and to special polarization effects such as polarization tuning in fiber lasers. Er-doped fibers tend to have larger birefringence and differential group delay than un-doped fibers. The larger values of the birefringence and its wavelength dependence can be used in the design of fiber laser. We show here measurements of the differential group delay and of the principal states of polarization, and their wavelength dependence, in short Er-doped fibers. In addition, we present the polarization characteristics for a round-trip propagation in a doped fiber. This last measurement can be used to analytically describe the tuning characteristics of a fiber laser with intra-cavity polarizer.
Quantum nondemolition measurements in optical fibers
Show abstract
Quantum non-demolition (QND) measurements are of great interest in recent years as a method to increase the information capacity of communication systems. Common implementations of QND measurements in optical fiber are based on the Kerr effect: a probe beam acquires phase modulation which mimics the amplitude modulation of a signal beam. This phase is typically small and needs to be measured at high frequencies for practical fiber-optic communication systems. Here we present a self reflexive interferometer scheme adequate for this kind of measurements and describe its performance. Using this system we achieved fairly open eye-diagrams at 140 Mbit/sec.
Tunable fiber lasers with birefringent fiber Bragg grating mirrors
Show abstract
A ring-type fiber laser with an external birefringent Bragg grating reflector is presented. The birefringent grating has a polarization-dependent transmission/reflection spectrum and by adjusting an intracavity polarization controller, a tunability range of 0.6 nm is achieved.
Remote Sensing of Targets and Backgrounds
Signal estimation in Bayesian field tracking
Robert G. Lindgren,
Robert W. Petersen
Show abstract
Bayesian field tracking, in which a posterior target distribution over the entire position-velocity state space, is a track-before-detect approach with a demonstrated capability to track at SNR levels below those for which the usual Kalman-based tracker is functional. Development of the Bayesian posterior probabilities is recursive and is driven by likelihood fields evaluated from successive measurement observations. Previous Bayesian field tracker applications have constructed likelihood fields assuming a prior signal amplitude distribution that has remained unchanged throughout processing. In this paper we combine a 1D Kalman filter with the diffusive projection of the Bayesian field tracker to estimate an amplitude distribution at each point of the state-space field. Results show that this approach can provide likelihood growth approaching that for a known signal amplitude.
Lasers, Nonlinear Optics, and Quantum Electronics
Absolute frequency stabilization of a 1.56-um laser by locking to sub-Doppler lines of Rb at 0.78 um
Vered Mahal,
Ariel Bruner,
Irena Kiryuschev,
et al.
Show abstract
A 1560 nm external cavity diode laser was efficiently doubled in a periodically poled LiNbO3 waveguide and locked to 87Rb sub-Doppler lines near 780 nm. Its frequency stability was characterized by measuring the beat frequency relative to a 780 nm external cavity diode laser which was locked to sub-Doppler lines of another Rb cell. The root Allan variance reached a minimum value of 6.9 X 10-12 in 1 s, which corresponded to frequency variations of 1.3 kHz for the 1560 nm laser.
Fiber Optics and Communications
Fiber Bragg grating analysis using the Floquet-Bloch approach
Show abstract
The Floquet-Bloch approach is utilized to analyze light propagation through fiber Bragg gratings. For sinusoidal gratings, the Mathieu equation is directly derived from the wave equation. The resulting stability diagram is then used to study the reflection and transmission properties of semi- infinite, as well as finite gratings. Bandwidth broadening and wavelength shifts with increasing UV exposure are demonstrated.
Strain sensing using embedded optical fibers and radio-frequency interferometry
Show abstract
An embedded optical fiber was used to measure the strain in a composite laminate. Strain was deduced from the induced propagation delay as measured by radio-frequency optical interferometry. The output of the optical sensor was found to follow the actual integrated average strain with some fluctuations which are attributed to polarization effects.
Optical Engineering
Benefits of a new converging beam scanning method for 8- to 12-um range imaging systems
Mark S. Shechterman
Show abstract
Most 8 - 12 micron infrared imaging optical systems consist of a telescope, angular scanner for parallel beams (polygon or nodding mirror type) and a detector lens. The telescope for all magnification modes, and the detector lens system, each one separately, have to be designed close to their diffraction limit over all scanned FOV to withstand the severe resolution requirements of the entire IR system. This fact mandates several aspherical surfaces for the telescope and the detector lens systems, for purposes of residual aberration correction. This paper describes an 8 - 12 micron FLIR in which, owing to the proposed lateral scanner for converging beams, the optical system is reduced to an objective only attached to the proposed lateral scanner which fulfills lateral scanning of the scenery image in the detector plane.
Fiber Optics and Communications
DOE-based wavelength multiplexing system for a single-mode image transmission
Show abstract
The expanding usage of optical communication via optical fibers and the situation of drastic increasing of the data required to be transmitted, urge the exploration of novel systems allowing to transmit high amount of spatial information by fiber with smaller spatial resolution. In this paper, optical encoding and decoding system is suggested for transmitting 1D or 2D images via a single mode fiber. The super resolving system is based on wavelength multiplexing of the input spatial information that is achieved with diffractive optical elements. Preliminary experimental results demonstrate the capabilities of the suggested method for the 1D case.
Optical Engineering
Differential rotationally shearing interferometer for optical testing of asymmetrical wavefronts
Show abstract
We present a theoretical basis for a new type of interferometer, a differential rotationally shearing interferometer. It differs from the traditional rotationally shearing interferometer in that the angle of rotation is infinitesimal or, at least, very small. A differential rotationally shearing interferometer may be used for the detection of wavefront asymmetry, even when this asymmetry is very small.
Additional Papers
Long-wavelength infrared 128 x 128 GaAs/GaAlAs multiple quantum well focal plane array
Shmuel I. Borenstain,
Uriel Arad,
I Lyubina,
et al.
Show abstract
We report on the fabrication and thermal imaging demonstration of a 128 by 128 focal plane array (FPA). The chip consists of an MBE grown GaAs/GaAlAs multiple quantum well (MQW) infrared detector matrix connected via indium columns to nodes of a mated readout multiplexer Si device. The electron intersubband to the continuum transition in the quantum well, created by the GaAs/GaAlAs conductive band discontinuity, is the mechanism responsible for the responsivity in the 6.5 micrometer - 8.5 micrometer spectral range. Pixels are 50 micrometer by 50 micrometer in size, spaced 60 micrometers apart. The pixel D* is 8 X 1010 cm(root)Hz/W which is the background limited performance (BLIP) at 77 K for a 180 degree field of view and background temperature of 300 K. The chip, packaged in a leadless chip carrier, was installed in variable temperature cryostat mounted with F/3 optics. The Si readout multiplexer having only 6 X 106 electrons (maximum) capacity of the integration well available to each pixel is the limiting factor in achieving a BLIP noise equivalent temperature difference (NETD). At an FPA operational temperature of 65 K, the measured NETD is 0.2 K.
Infrared microantennas
Show abstract
We present results of measurements of the polarization response of asymmetric spiral antennas
coupled to Ni-NiO-Ni diodes, over the wavelength range 10.2 to 10.7 tim. The feed structure of the
antenna imposes an elliptical polarization signature that is different from the circular polarization expected
from a symmetric spiral. We develop a lossy-transmission-line model yielding the measured polarization
response. A combination of a balanced and an unbalanced mode is required. Reflected current waves
from the arm ends are significant.