This PDF file contains the front matter associated with SPIE Proceedings Volume 8374, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

In recent years there has been great progress in the Laser Induced Breakdown Spectroscopy (LIBS) technology field. Significant advances have been made both in fundamental and applied research as well as in data processing/chemometrics. Improvements in components, most notably lasers/optics and spectrometers are enabling the development of new devices that are suitable for field use. These new commercial devices recently released to the marketplace, as well as ones currently under development, are bringing the potential of LIBS for CBRNE threat analysis into real-world applications.

Raman spectroscopy, when used in spatially offset mode, has become a potential tool for the identification of explosives and other hazardous substances concealed in opaque containers. The molecular fingerprinting capability of Raman spectroscopy makes it an attractive tool for the unambiguous identification of hazardous substances in the field. Additionally, minimal sample preparation is required compared with other techniques. We report a field portable time resolved Raman sensor for the detection of concealed chemical hazards in opaque containers. The new sensor uses a pulsed nanosecond laser source in conjunction with an intensified CCD detector. The new sensor employs a combination of time and space resolved Raman spectroscopy to enhance the detection capability. The new sensor can identify concealed hazards by a single measurement without any chemometric data treatments.

While substantial progress has been made recently towards the miniaturization of Raman, mid-infrared (IR), and near-infrared (NIR) spectrometers, there remains continued interest from end-users and product developers in pushing the technology envelope toward even smaller and lower cost analyzers. The potential of these instruments to revolutionize on-site and on-line applications can only be realized if the reduction in size does not compromise performance of the spectrometer beyond the practical need of a given application. In this paper, the working principle of a novel, extremely miniaturized NIR spectrometer will be presented. The ultra-compact spectrometer relies on thin-film linear variable filter (LVF) technology for the light dispersing element. We will also report on an environmental study whereby the contamination of soil by oil is determined quantitatively in the range of 0-12% by weight of oil contamination. The achieved analytical results will be discussed in terms of the instrument's competitiveness and suitability for on-site and in-the-field measurements.

FT-IR spectroscopy is the technology of choice to identify solid and liquid phase unknown samples. The challenges of ConOps (Concepts of Operation) in emergency response and military field applications require a significant redesign of the stationary FT-IR bench-top instruments typically used in laboratories. Specifically, field portable units require high levels of resistance against mechanical shock and chemical attack, ease of use in restrictive gear, quick and easy interpretation of results, and reduced size. In the last 20 years, FT-IR instruments have been re-engineered to fit in small suitcases for field portable use and recently further miniaturized for handheld operation. This article introduces the advances resulting from a project designed to overcome the challenges associated with miniaturizing FT-IR instruments. The project team developed a disturbance-corrected permanently aligned cube corner interferometer for improved robustness and optimized opto-mechanical design to maximize optical throughput and signal-to-noise ratios. Thermal management and heat flow were thoroughly modeled and studied to isolate sensitive components from heat sources and provide the widest temperature operation range. Similarly, extensive research on mechanical designs and compensation techniques to protect against shock and vibration will be discussed. A user interface was carefully created for military and emergency response applications to provide actionable information in a visual, intuitive format. Similar to the HazMatID family of products, state-of-the-art algorithms were used to quickly identify the chemical composition of complex samples based on the spectral information. This article includes an overview of the design considerations, tests results, and performance validation of the mechanical ruggedness, spectral, and thermal performance.

Terahertz (THz) time-domain spectroscopy has proven to be a promising technology for a wide range of applications, such as inspection of nished products or materials, quality control, biomedical imaging and diagnostics, counterfeit detection and characterization of semiconductors. This paper investigates the applicability of THz time-domain spectroscopy for the characterization of silicon solar cell properties such as: conductivity, charge carrier mobility and density. Moreover, the possibilities for THz spectroscopy and imaging for the defect analysis in semiconductor and photovoltaic materials are investigated. THz-pump/THz-probe measurements were carried out on silicon wafers which were illuminated by a halogen light source to inject free charge carriers. Initial results indicate that THz time-domain spectroscopy is a promising technique for the characterization of silicon wafers for the photovoltaic industry.

The absolute spectral radiant exitance of IR signatures from countermeasure flares for mid-IR was experimentally validated by using an optical emission spectrometer. A 256-array PbSe detector was installed to analyze the mid-IR emission spectrum of four IR signatures from countermeasure flares and propellants. We could evaluate the performance of the optical emission spectrometer and verify its usefulness in the field of IR countermeasures. The spectral response of the optical emission spectrometer was calibrated using a directly heated graphite blackbody; in addition, the total uncertainty was analyzed. The absolute amount of emissions of four IR signatures was calculated and compared.

VTT Technical Research Centre of Finland has developed a Fabry-Perot Interferometer (FPI) based hyperspectral imager compatible with light weight UAV (Unmanned Aerial Vehicle) platforms (SPIE Proc. 7474¹, 8186B²). The FPI based hyperspectral imager was used in a UAV imaging campaign for forest and agriculture tests during the summer 2011 (SPIE Proc. 8174³). During these tests high spatial resolution Color-Infrared (CIR) images and hyperspectral images were recorded on separate flights. The spectral bands of the CIR camera were 500 - 580 nm for the green band, 580 - 700 nm for the red band and 700 - 1000 nm for the near infrared band. For the summer 2012 flight campaign a new hyperspectral imager is currently being developed. A custom made CIR camera will also be used. The system which includes both the high spatial resolution Color-Infrared camera and a light weight hyperspectral imager can provide all necessary data with just one UAV flight over the target area. The new UAV imaging system contains a 4 Megapixel CIR camera which is used for the generation of the digital surface models and CIR mosaics. The hyperspectral data can be recorded in the wavelength range 500 - 900 nm at a resolution of 10 - 30 nm at FWHM. The resolution can be selected from approximate values of 10, 15, 20 or 30 nm at FWHM.

Traditionally, XRD had been used to study the crystalline structure of cotton celluloses. Despite considerable efforts in developing the curve-fitting protocol to evaluate the crystallinity index (CI), in its present state, XRD measurement can only provide a qualitative or semi-quantitative assessment of the amounts of crystalline and amorphous cellulosic components in a sample. The greatest barrier to establish quantitative XRD is the lack of appropriate cellulose standards needed to calibrate the measurements. In practical, samples with known CIs are very difficult to be prepared or determined. As an approach, we might assign the samples with reported CIs from FT-IR procedure, in which the threeband ratios were first calculated and then were converted into CIs within a large and diversified pool of cotton fibers. This study reports the development of simple XRD algorithm, over time-consuming and subjective curve-fitting process, for direct determination of cotton cellulose CI by correlating XRD with the FT-IR CI references.

Hyperspectral imaging (HSI) sensors allow standoff visualization and identification of chemical vapor plumes; however, currently available COTS sensors, which produce very high quality data, are expensive(>$750k), large(>100 L), and massive( >30 kg). Man-portable and UAV based hyperspectral sensor applications require smaller and lighter weight designs. An approach using new technologies, including a microbolometer IR camera, a piezo-electric linear actuator, a FPGA/LAN board, and an embedded multi-core CPU, is presented that seeks to produce similar quality hyperspectral data at a 10x cost reduction, 3x size reduction (<30 L), and a 3x mass reduction (<10 kg for optics and electronics). The design challenges, system overview, and initial performance data measurements from the new spectrometer designs are presented. An overview of the data cube signal processing, including spatial co-adding, re-sampling of the interferogram data point spacing, phase correction, and detection algorithms, is presented. The spectrometer optical design was also tested by temporarily installing a single pixel MCT detector in order to make spectral resolution comparisons with a traditional FTIR spectrometer.

Hyperspectral imaging has important benefits in remote sensing and target discrimination applications. This paper describes a class of snapshot-mode hyperspectral imaging systems which utilize a unique optical processor that provides video-rate hyperspectral datacubes. This system consists of numerous parallel optical paths which collect the full threedimensional (two spatial, one spectral) hyperspectral datacube with each video frame and are ideal for recording data from transient events, or on unstable platforms. We will present the results of laboratory and field-tests for several of these imagers operating at visible, near-infrared, MWIR and LWIR wavelengths. Measurement results for nitrate detection and identification as well as additional chemical identification and analysis will be presented.

Material discrimination based on conventional or dual energy X-ray computed tomography (CT) imaging can be ambiguous. X-ray diraction imaging (XDI) can be used to construct diraction proles of objects, providing molecular signature information that can be used to characterize the presence of specic materials. Combining X-ray CT and diraction imaging can lead to enhanced detection and identication of explosives in luggage screening. Current XDI scan systems are based on direct imaging rather than tomographic imaging, which require the use of line collimators to localize scattering location and thus result in slow scan performance. In an eort to gain faster scan times and better signal-to-noise ratio, we focus on tomographic inversion techniques for X-ray Diraction Tomography (XDT) and look for joint reconstruction of CT absorption and X-ray diraction prole images of object. We present a fast reconstruction algorithm with geometric feature preserving regularization (IREP) using image-wise based iterative coordinate descent (ICD).We validate the initial results via Monte Carlo simulation of X-ray absorption and coherent scattering in 2 dimensions (2D), and compare the performance of the IREP algorithm with existing inversion techniques such as the ltered backprojection method and the algebraic reconstruction technique. The experimental results show that the IREP method oers improved image quality for enhanced material identication.

Several chemical compounds have their strongest spectral signatures in the thermal region. This paper presents three push-broom thermal hyperspectral imagers. The first operates in MWIR (2.8-5 μm) with 35 nm spectral resolution. It consists of uncooled imaging spectrograph and cryogenically cooled InSb camera, with spatial resolution of 320/640 pixels and image rate to 400 Hz. The second imager covers LWIR in 7.6-12 μm with 32 spectral bands. It employs an uncooled microbolometer array and spectrograph. These imagers have been designed for chemical mapping in reflection mode in industry and laboratory. An efficient line-illumination source has been developed, and it makes possible thermal hyperspectral imaging in reflection with much higher signal and SNR than is obtained from room temperature emission. Application demonstrations including sorting of dark plastics and mineralogical mapping of drill cores are presented. The third imager utilizes a cryo-cooled MCT array with precisely temperature stabilized optics. The optics is not cooled, but instrument radiation is suppressed by special filtering and corrected by BMC (Background-Monitoring-on-Chip) method. The approach provides excellent sensitivity in an instrument which is portable and compact enough for installation in UAVs. The imager has been verified in 7.6 to 12.3 μm to provide NESR of 18 mW/(m² sr μm) at 10 μm for 300 K target with 100 spectral bands and 384 spatial samples. It results in SNR of higher than 500. The performance makes possible various applications from gas detection to mineral exploration and vegetation surveys. Results from outdoor and airborne experiments are shown.

The trend in the development of single-point spectrometric sensors is miniaturization, cost reduction and increase of functionality and versatility. MEMS Fabry-Perot interferometers (FPI) have been proven to meet many of these requirements in the form of miniaturized spectrometer modules and tuneable light sources. Recent development of MEMS FPI devices based on ALD thin film structures potentially addresses all of these main trends. In this paper we present a device and first measurement results of a small imaging spectrometer utilizing a 1.5 mm tuneable MEMS FPI filter working in the visible range of 430-580 nm. The construction of the instrument and the properties of the tuneable filter are explained especially from imaging requirements point of view.

Volume Bragg grating technology has enabled the development of a new type of staring hyperspectral camera. Based on Bragg Tunable filters, these hyperspectral cameras have both high spectral and spatial resolution, and significantly higher sensitivity than competing technologies like push broom spectrometer, liquid crystal tunable filters, or acousto-optic tunable filters. They are minimally sensitive to polarization and their spectral isolation can reach 10⁶. Here we thus present an innovative tool to collect SWIR hyperspectral data with high spectral and spatial resolution. This new instrument is based on a 3nm bandwidth Bragg Tunable Filter, continuously tunable from 1.0um and 2.5um. Because high spectral resolution also means less light per channel, a low noise custom HgCdTe (MCT) camera was also developed to meet the requirement of the filter. The high speed capability of more than 300 fps and the low operating temperature of 200K (deep cooled option to 77K) allow full frame 500 spectral channel datacube acquisitions in minimal time. Basic principle of this imaging filter will be reviewed as well as the custom MCT camera performances. High resolution hyperspectral measurements will be demonstrated between 1.0um and 2.5um on different objects.

The performance of mid-IR interband cascade lasers (ICLs) has been improved by introducing heavier doping into the electron injector regions with the purpose of increasing the electron density in the active region to the level commensurate with the active hole density. For devices emitting at wavelengths in the 3.6-3.9 μm range, the improvements include pulsed room temperature (RT) threshold current density as low as 170 A/cm², maximum cw operating temperature as high as 109 °C, and RT cw input power as low as 29 mW. Epi-down-mounted ridges display RT cw wall-plug efficiencies as high as 14.6% as well as emission of > 200 mW into a nearly diffraction-limited beam. RT cw operation has also been demonstrated for considerably longer wavelengths extending to 5.7 μm with threshold power densities of ≈1kW/cm2, which are an order of magnitude lower than those in state-of-theart quantum cascade lasers. The very low operating powers are expected to lengthen battery lifetimes and greatly relax packaging and size/weight requirements for fielded chemical-sensing systems.

We are developing prototype chip-scale low-power integrated-optic gas-phase chemical sensors based on infrared Tunable Diode Laser Absorption Spectroscopy (TDLAS). TDLAS is able to sense many gas phase chemicals with high sensitivity and selectivity. Using semiconductor fabrication and assembly techniques, the low-cost integrated optic TDLAS technology will permit mass production of sensors that have wide ranging industrial, medical, environmental, and consumer applications. Novel gas sensing elements using low-loss resonant photonic crystal cavities or waveguides will permit monolithic integration of a laser source, sampling elements, and detector on a semiconductor materials system substrate. Practical challenges to fabricating these devices include: a) selecting and designing the high-Q micro-resonator sensing element appropriate for the selected analyte; and b) device thermal management, especially stabilizing laser temperature with the precision needed for sensitive spectroscopic detection. In this paper, we analyze the expected sensitivity of micro-resonator-based structures for chemical sensing, and demonstrate a novel approach for exploiting laser waste heat to stabilize the laser temperature.

Maxion Technologies has designed a monolithic, widely tunable Quantum Cascade (QC) laser for use in chemical sensing applications. This multi-section QC laser is a monolithically tunable device, similar to those demonstrated in the near IR for telecommunications. Wideband tuning is achieved through grating assisted coupling of the optical mode between lateral waveguides, allowing ~10 times the tuning range normally achieved by distributed feedback lasers without incorporation of external optical elements. Compared to implementations in the near IR, the use of lateral waveguides (rather than vertically stacked waveguides) allows the optical mode to maintain the high overlap with the active region necessary for room temperature lasing in the mid-IR. Due to its monolithic design, this laser is expected to be rapidly tunable and usable in field environments due to its insensitivity to shock and vibration, while the wide tuning range of the device will allow for an enhanced ability to discriminate against background chemicals.

Semiconductor laser performance in the 3 to 4 micron wavelength region has lagged behind lasers at longer and shorter wavelengths. However, recent advances by the group at the Naval Research Laboratory (NRL) have markedly changed this situation, and in a recent collaboration with the NRL group, we demonstrated high performance interband cascade lasers at 3.8 microns. In this work, we present results extending this earlier work to shorter wavelengths. In particular, we designed four new interband cascade lasers at target wavelengths between 3.3 and 3.5 microns. Initial testing of broad area devices show threshold current densities of ~230 A/cm² at 300K, almost a factor of two lower than the ~425 A/cm² results obtained on the broad area devices at 3.8 microns. In this paper, we present performance data on these broad area lasers and also data on narrow ridge devices fabricated from the same material.

The requirements for standoff detection of Explosives and CWA/TICs on surfaces in the battlefield are challenging because of the low detection limits. The variety of targets, backgrounds and interferences increase the challenges. Infrared absorption spectroscopy with traditional infrared detection technologies, incandescent sources that offer broad wavelength range but poor spectral intensity, are particularly challenged in standoff applications because most photons are lost to the target, background and the environment. Using a brighter source for active infrared detection e.g. a widely-tunable quantum cascade laser (QCL) source, provides sufficient spectral intensity to achieve the needed sensitivity and selectivity for explosives, CWAs, and TICs on surfaces. Specific detection of 1-10 μg/cm² is achieved within seconds. CWAs, and TICs in vapor and aerosol form present a different challenge. Vapors and aerosols are present at low concentrations, so long pathlengths are required to achieve the desired sensitivity. The collimated output beam from the QCL simplifies multi-reflection cells for vapor detection while also enabling large standoff distances. Results obtained by the QCL system indicate that <1 ppm for vapors can be achieved with specificity in a measurement time of seconds, and the QCL system was successfully able to detect agents in the presence of interferents. QCLs provide additional capabilities for the dismounted warfighter. Given the relatively low power consumption, small package, and instant-on capability of the QCL, a handheld device can provide field teams with early detection of toxic agents and energetic materials in standoff, vapor, or aerosol form using a single technology and device which makes it attractive compared other technologies.

In this paper we present a time-gated single-photon avalanche diode (SPAD) array, the first of its kind to be integrated with a newly developed time-resolved laser Raman spectrometer. Time-resolved Raman spectra from various highly fluorescent minerals were successfully observed using our SPAD array; these spectra were obscured by an overwhelming fluorescence background when measured using a traditional continuous wave green laser. The system has photon detection efficiency (PDE) of 5 % at 5 V excess bias with on-chip microlenses. The dark count rate (DCR) of this SPAD is 1.8 kHz at 5 V excess bias. However, thanks to the nanosecond scale time-gating, noise rate per frame is effectively reduced to ~10^-3 counts at 40 kHz laser repetition rate.

In the past few years, there has arisen an intense demand for new generation technologies which provide for the rapid and sensitive stand-off detection of explosive compounds and hazardous chemicals. This has been fueled, in large part, by the escalation of threats to homeland security and the debilitating effects of IED devices in both civilian and war zones. In this paper, we describe two portable stand-off Raman spectrometers which have been developed by DeltaNu and are intended for use in different test environments. The first, the DeltaNu ObserveR™, is a handheld785 nm laser device suited for the close range detection of explosive materials during nighttime operations, or indoors under restricted light conditions. The second device, the ObserveR LR, is a tripod-mounted, solar blind system that enables detection at longer distances (ca. <30 m) with reduced fluorescence interference. A condensed summary is presented of different tests that have been conducted using these devices, and results are discussed within the context of technological improvements that will be required to adequately meet the challenge of robust explosive material detection.

We demonstrate a fiber-optic Raman probe based on single-crystal sapphire fibers to overcome the large background signal of Raman probes based on standard glass fibers. Using 514.5 nm and 785 nm excitation lasers, Raman spectroscopy was performed on samples of calcite, aqueous sodium carbonate solution, and silicon wafer using a single crystal sapphire fiber and a silica fiber of similar lengths and numerical apertures. The single-crystal sapphire fiber exhibits narrow Raman peaks and low background signal, allowing for the detection of weaker Raman signals or Raman signals located in the lower wavenumber region, while the traditional silica fiber has a strong broadband Raman spectrum of its own.

The use of portable Raman analyzers to identify unknown substances in the field has grown dramatically during the past decade. Measurements often require the laser beam to exit the confines of the sample compartment, which increases the potential of eye or skin damage. This is especially true for most commercial analyzers, which use 785 nm laser excitation. To overcome this safety concern, we have built a portable FT-Raman analyzer using a 1550 nm retina-safe excitation laser. Excitation at 1550 nm falls within the 1400 to 2000 nm retina-safe range, so called because the least amount of damage to the eye occurs in this spectral region. In contrast to wavelengths below 1400 nm, the retina-safe wavelengths are not focused by the eye, but are absorbed by the cornea, aqueous and vitreous humor. Here we compare the performance of this system to measurements of explosives at shorter wavelengths, as well as its ability to measure surface-enhanced Raman spectra of several chemicals, including the food contaminant melamine.

A Raman mapping system for detecting and discriminating minerals such as dolomite, marble, calcite and pyrite is demonstrated. The system is built from components that are suitable for industrial conditions. Together with a signal processing and a classier the system was shown to be capable of discriminating between several important classes of mineral. The technique is a potential alternative to sensing methods currently used for mineral sorting.

Fourier transform interferometry is commonly performed by means of mechanically scanning interferometers such as a Michelson and characterized by one scanning mirror. This results in severe limitations of the capability of measuring fast signals. To overcome this drawback, we present a multi-channel FTIR spectrometer (MC-FTIR) that is capable of single-shot operation no matter how short the single pulse is, provided it delivers sufficient photons for the signal to exceed the noise. It can capture fast transient signals, limited by the signal-to-noise ratio and data transfer rate of the detector. Our device is based on a micro/nanomanufactured 3D multimirror array (MMA) which allows collecting a whole interferogram simultaneously. MMAs are manufactured by means of a patented multiple moving mask grey-level deep X-ray lithography process. Up to 640 mirror cells, generating optical path differences from 0 to about 1 mm, were achieved so far at optical quality. We have demonstrated sub-millisecond pulses and a theoretical spectral resolution of 10 cm^-1 in the mid-IR. The optical system is similar to a Czerny-Turner mount with the MMA replacing the grating and an MCT focal plane array (FPA) capturing the interferogram. Our MC-FTIR enables extension of FTIR-based IR spectroscopy to arbitrarily short pulses and to fast transient signals. As the optical system is small and rugged, the instrument lends itself readily to field applications. Ongoing work is aimed at emerging applications including biomedical, laser-induced breakdown spectroscopy, and spectroscopy of synchrotron radiation.

OPTRA is in the process of completing the development of a high speed resonant Fourier transform infrared (HSR-FTIR) spectrometer in support of the Army's thermal luminescence measurements of contaminants on surfaces. Our system employs a resonant scanning mirror which enables 6.2 kHz spectral acquisition rate with 27 cm^-1 spectral resolution over the 700 to 1400 cm^-1 spectral range. The design is ultimately projected to achieve a 10 kHz spectral acquisition rate with 8 cm^-1 spectral resolution over the same spectral range. To date this system represents the highest/broadest combination of spectral acquisition rate and spectral range available. Our paper reports on the final design, build, and test of the HSR-FTIR prototype spectrometer system. We present a final radiometric analysis predicting system performance along with the details of the signal channel conditioning which addresses the effects of the high speed sinusoidal scanning. We present the final opto-mechanical design and the high speed interferogram acquisition scheme. We detail the system build and integration and describe the tests that will be performed to characterize the instrument. Finally, we offer a list of future improvements of the HSR-FTIR system.

The classic trade-off between resolution and throughput in a dispersive spectrometer is overcome using virtual slit technology. An optimized spectrometer designed from the ground up to incorporate a virtual slit is experimentally demonstrated by Raman experiments.

Spectrometers and Spectrographs based on scanning grating monochromators are well-established tools for various applications. As new applications came into focus in the last few years, there is a demand for more sophisticated and miniaturized systems. The next generation spectroscopic devices should exhibit very small dimensions and low power consumption, respectively. We have developed a spectroscopic system with a volume of only (15 × 10 × 14) mm³ and a few milliwatts of power consumption that has the potential to fulfill the demands of the upcoming applications. Our approach is based on two dierent strategies. First, we apply resonantly driven MEMS (micro electro mechanical systems). The latest generation of our MEMS scanning grating device has two integrated optical slits and piezoresistive position detection in addition to the already existing miniaturized 1-d scanning grating plate and the electrostatic driving mechanism. Our second strategy is to take advantage of the hybrid integration of optical components by highly sophisticated manufacturing technologies. One objective is the combination of MEMS technology and a planar mounting approach, which potentially facilitate the mass production of spectroscopic systems and a signicant reduction of cost per unit. We present the optical system design as well as the realization of a miniaturized scanning grating spectrometer for the near infrared (NIR) range between 950 nm and 1900 nm with a spectral resolution of 10 nm. The MEMS devices as well as the optical components have been manufactured and rst samples of the spectroscopic measurement device have been mounted by an automated die bonder.

As is generally known, miniature infrared spectrometers have great potential, e. g. for process and environmental analytics or in medical applications. Many efforts are being made to shrink conventional spectrometers, such as FTIR or grating based devices. A more rigorous approach for miniaturization is the use of MEMS technologies. Based on an established design for the MWIR new MEMS Fabry-Perot filters and sensors with expanded spectral ranges in the LWIR have been developed. The range 5.5 - 8 μm is particularly suited for the analysis of liquids. A dual-band sensor, which can be simultaneously tuned from 4 - 5 μm and 8 - 11 μm for the measurement of anesthetics and carbon dioxide has also been developed. A new material system is used to reduce internal stress in the reflector layer stack. Good results in terms of finesse (≤ 60) and transmittance (≤ 80 %) could be demonstrated. The hybrid integration of the filter in a pyroelectric detector results in very compact, robust and cost effective microspectrometers. FP filters with two moveable reflectors instead of only one reduce significantly the acceleration sensitivity and actuation voltage.

Recently, we have demonstrated a hybrid diffractive optical element that combines the dispersion function of a grating and the focusing function of a Fresnel lens (G-Fresnel) into a single device. The G-Fresnel promises a low f-number enabling miniaturization of a spectrometer system while maintaining high spectral resolution. A proof-of-concept G-Fresnel based spectrometer is demonstrated, yielding sub-nanometer resolution. Due to its compactness and low-cost fabrication technique, the G-Fresnel based spectrometer has the potential for use in mobile platforms such as lab-on-a-chip microfluidic devices and other mobile spectrometer applications.

Conventional optical spectrometers that are based on bulk optical components tend to be relatively large and expensive compared to the other components used in systems designed for detecting chemical/biological agents. Microspectrometers based on focusing waveguide gratings incorporate both spectral dispersion and focusing functions into a single component that can be fabricated hundreds at a time at the wafer level using nano-imprint lithography techniques. These types of spectrometers are ideal for integration into micro-fluidic systems because the signals can be directly coupled into the planar waveguide. We present preliminary data from a prototype system and explore potential applications for these devices.

OPTRA has developed a novel approach to phase shift cavity ring down spectroscopy (PS-CRDS) using a Fourier transform infrared (FTIR) modulator to impose the spectrally-dependent amplitude modulation on a broadband IR light source. As with previous PS-CRDS measurements, we excite a resonant cavity with amplitude modulated energy and measure the phase shift of the modulated signal exiting the cavity which is proportional to the ring down time and inversely proportional to the losses of the cavity including those due to molecular absorption. In contrast to previous efforts, we impose the amplitude modulation with the FTIR interferometer instead of an external electro-optical modulator and extract the phase from each interferogram thereby enabling broadband FTIR-PS-CRDS measurements at greater than 1 Hz update rates. The measured phase spectra can then be used for multicomponent analysis. The combined measurement can be viewed as a resonant cavity enhancement to traditional FTIR spectroscopy or a broadband enhancement to CRDS. In our paper we present the theory behind this measurement and describe the breadboard and test results from our feasibility study.

There is a growing need for new characterization techniques that can provide information about the chemical composition of surfaces and bulk materials with spatial resolution in the range of 1-10 microns. While FTIR microspectroscopy addresses this problem, the practical resolution limit is still only about 20 microns. Other well-established techniques at the nanometer are impractical at the micro-scale. Raman micro-spectroscopy provides adequate spatial resolution (~1 micron), but may not always be useful due to its low throughput and for samples with strong fluorescence. We are developing a non-contact and non-destructive technique that provides similar information as IR or Raman spectroscopy. It involves photo-thermal heating of the sample with a tunable quantum cascade laser (or other suitable infrared laser) and measuring the resulting increase in thermal emission by either an infrared detector or a laser probe in the visible spectral range. The latter case allows for further increase of the spatial resolution from ~10 microns to ~1 micron, at the right experimental conditions. Since the thermal emission signal from the surface is directly proportional to the absorption coefficient, by tuning the laser wavelength we directly measure the IR spectrum of the sample. By raster-scanning over the surface of the sample we can obtain chemical composition maps. We demonstrate this technique by imaging the surface of several different materials. We analyze the spatial resolution of our photo-thermal imaging system as well as discuss the conditions under which the spatial resolution can be further increased from the infrared far-field diffraction limit.

We present a CTIS system that uses an optimized diffractive optical element (DOE) to project the spectral and spatial information simultaneously onto a CCD. We compare the DOE with and older approach based on glass gratings and found that the DOE gave an improved spectral response. We argue that a DOE is the most effective approach for CTIS.

The article describes an application of cavity enhanced absorption spectroscopy for nitric oxide and nitrous oxide detection. Both oxides are important greenhouse gases that are of large influence on environment, living organisms and human health. These compounds are also biomarkers of some human diseases. They determine the level of acid rain, and can be used for characterization of specific explosive materials. Therefore the sensitive detectors of these gases are of great importance for many applications: from routine air monitoring in industrial and intensive traffic areas, to detection of explosives in airports, finally for medicine investigation, for health care, etc. Our compact detection system provides opportunity for simultaneous measure of both NO and N₂O concentration at ppb level. Its sensitivity is comparable with sensitivities of instruments based on other methods, e.g. gas chromatography or mass spectrometry.