This PDF file contains the front matter associated with SPIE Proceedings Volume 8726, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

The High Throughput Virtual Slit (or HTVS) is a new optical technology which can significantly increase the throughput and resolution of a dispersive spectrometer. The HTVS is able to preserve spectrometer étendue, mitigating photon losses normally associated with a slit. Originally implemented in multimode fiber-input spectrometers, HTVS has now been shown to be broadly applicable to a wide variety of spatially scanning hyperspectral imagers and standoff sensors, enhancing their performance and unlocking new application areas. In essence, the anamorphic elements of the HTVS optical system provide a means to decouple the spatial (iFOV) and spectral resolution of nearly any HSI system. In some scenarios, HTVS can be used to achieve better spectral resolution with the same input slit width. Alternatively, the slit can be widened (to increase the collected signal) while maintaining the same spectral resolution. This newfound flexibility in optimizing critical performance parameters not only improves the performance of HSI systems in existing remote sensing contexts, but also opens up numerous new application areas which were previously inaccessible to hyperspectral techniques. This method adds substantial value to existing HSI designs, particularly in applications involving targets with large spatial extent and requiring high spectral resolution (e.g. standoff Raman spectroscopy). We present recent experimental results from our prototype HTVS pushbroom imager and discuss case studies of standoff Raman detection of hazardous materials, passive detection of faint narrowband and monochromatic sources, and optimal disentangling of target spectral signatures from the solar spectrum under daytime illumination.

The utility of Hyper Spectral Imaging (HSI) passive chemical detection employing wide field, standoff imaging continues to be advanced in detection applications. With a drive for reduced SWaP (Size, Weight, and Power), increased speed of detection and sensitivity, developing a handheld platform that is robust and user-friendly increases the detection capabilities of the end user. In addition, easy to use handheld detectors could improve the effectiveness of locating and identifying threats while reducing risks to the individual. ChemImage Sensor Systems (CISS) has developed the HSI Aperio™ sensor for real time, wide area surveillance and standoff detection of explosives, chemical threats, and narcotics for use in both government and commercial contexts. Employing liquid crystal tunable filter technology, the HSI system has an intuitive user interface that produces automated detections and real-time display of threats with an end user created library of threat signatures that is easily updated allowing for new hazardous materials. Unlike existing detection technologies that often require close proximity for sensing and so endanger operators and costly equipment, the handheld sensor allows the individual operator to detect threats from a safe distance. Uses of the sensor include locating production facilities of illegal drugs or IEDs by identification of materials on surfaces such as walls, floors, doors, deposits on production tools and residue on individuals. In addition, the sensor can be used for longer-range standoff applications such as hasty checkpoint or vehicle inspection of residue materials on surfaces or bulk material identification. The CISS Aperio™ sensor has faster data collection, faster image processing, and increased detection capability compared to previous sensors.

VTT Technical Research Centre of Finland has developed microelectromechanical (MEMS) Fabry-Perot interferometer (FPI) for hydrocarbon measurements. Fabry-Perot interferometer is a structure where is two highly reflective surfaces separated by a tunable air gap. The MEMS FPI is a monolithic device, i.e. it is made entirely on one substrate in a batch process, without assembling separate pieces together. The gap is adjusted by moving the upper mirror with electrostatic force, so there are no actual moving parts. The manufactured MEMS FPIs have been characterized. The tuning wavelength range of the MEMS FPI is 2.8-3.5 μm and its spectral resolution is 50-60 nm. VTT has designed and manufactured a handheld size demonstrator device based on the technology presented in this abstract. This device demonstrates gas detecting by measuring cigarette lighter gas and various plastic materials transmission spectra. The demonstrator contains light source, gas cell, MEMS FPI, detector and control electronics. It is connected to a laptop by USB connection, additional power supply or connection is not needed.

Grating spectrometers have been designed in many different configurations. Now potential high volume applications ask for extremely miniaturized and low cost systems. By the use of integrated MEMS (micro electro mechanical systems) scanning grating devices a less expensive single detector can be used in the NIR instead of the array detectors required for fixed grating systems. Meanwhile the design of a hybrid integrated MEMS scanning grating spectrometer has been drawn. The MEMS device was fabricated in the Fraunhofer IPMS own clean room facility. This chip is mounted on a small circuit board together with the detector and then stacked with spacer and mirror substrate. The spectrometer has been realized by stacking several planar substrates by sophisticated mounting technologies. The spectrometer has been designed for the 950nm – 1900nm spectral range and 9nm spectral resolution with organic matter analysis in mind. First applications are considered in the food quality analysis and food processing technology. As example for the use of a spectrometer with this performance the grill process of steak was analyzed. Similar measurement would be possible on dairy products, vegetables or fruit. The idea is a mobile spectrometer for in situ and on site analysis applications in or attached to a host system providing processing, data access and input-output capabilities, disregarding this would be a laptop, tablet, smart phone or embedded platform.

Nitric oxide (NO) is a major chemical byproduct of many photochemically active nitrogen-containing compounds. As a prototypical free radical with a very well characterized high-resolution spectrum, NO provides a standard spectroscopic fingerprint for indirect quantitative analysis and detection of a number of low vapor pressure nitroaromatic compounds in air through either direct photochemical decomposition of a parent molecule or from its relatively high vapor pressure chemical constituents. In this paper, we will discuss applications of picosecond laser spectroscopy for measurements and detection of NO and the nascent NO generated from photolysis of nitrobenzene. We will give a general overview of our tunable picosecond laser and detection system that we routinely use for probing and exciting the NO gamma band. This broad wavelength tuning capability of our laser allows us to set up pump-probe type experiments for detecting blue shifted rovibronic bands and probing the relative population distribution for NO. In all cases, experiments were performed using UV laser pulses of duration less than 20 ps. Also, we studied the effect of N₂ collisions on the photoframentation spectrum of nitrobenzene in 1000 mbar of N₂ buffer gas.

Laser sensing enables aerial detection of natural gas pipeline leaks without need to fly through a hazardous gas plume. This paper describes adaptations of commercial laser-based methane sensing technology that provide relatively low-cost lightweight and battery-powered aerial leak sensors. The underlying technology is near-infrared Standoff Tunable Diode Laser Absorption Spectroscopy (sTDLAS). In one configuration, currently in commercial operation for pipeline surveillance, sTDLAS is combined with automated data reduction, alerting, navigation, and video imagery, integrated into a single-engine single-pilot light fixed-wing aircraft or helicopter platform. In a novel configuration for mapping landfill methane emissions, a miniaturized ultra-lightweight sTDLAS sensor flies aboard a small quad-rotor unmanned aerial vehicle (UAV).

We present experimental demonstration of a new chemical sensing technique based on intracavity absorption in an external cavity quantum cascade laser (ECQCL). This new technique eliminates the need for an infrared photodetector and gas cell by detecting the intracavity absorption spectrum in the compliance voltage of the laser device itself. To demonstrate and characterize the technique, we measure infrared absorption spectra of chemicals including acetone and Freon-134a. Sub-ppm detection limits in one second are achieved, with the potential for increased sensitivity after further optimization. The technique enables development of handheld, high-sensitivity, and high-accuracy trace gas sensors for in-field use.

Conventional mid-infrared (mid-IR) Fourier transform infrared (FT-IR) spectroscopic imaging systems employ an incoherent globar source and achieve spectral contrast through interferometry. While this approach is suitable for many general applications, recent advancements in broadly tunable external cavity Quantum Cascade Lasers (QCL) offer new approaches to and new possibilities for mid-IR micro-spectroscopic imaging. While QCL-based devices have yet to achieve the wide spectral range generally employed by spectroscopists for molecular analyses, they are starting to be used for microscopy at discrete frequencies. Here, we present a discrete frequency IR (DFIR) microscope based on a QCL source and explore its utility for mid-IR imaging. In our prototype instrument, spectral contrast is achieved by tuning the QCL to bands in a narrow spectral region of interest. We demonstrate wide-field imaging employing a 128x128 pixel liquid nitrogen cooled mercury cadmium telluride (MCT) focal plane array (FPA) detector. The resulting images demonstrate successful imaging as well as several unique features due to coherence effects from the laser source. Here we discuss the effects of this coherence and compare our instrument to conventional mid-IR imaging instrumentation.

Portable analytical devices based on a gamut of technologies (Infrared, Raman, X-Ray Fluorescence, Mass Spectrometry, etc.) are now widely available. These tools have seen increasing adoption for field-based assessment by diverse users including military, emergency response, and law enforcement. Frequently, end-users of portable devices are non-scientists who rely on embedded software and the associated algorithms to convert collected data into actionable information. Two classes of problems commonly encountered in field applications are identification and screening. Identification algorithms are designed to scour a library of known materials and determine whether the unknown measurement is consistent with a stored response (or combination of stored responses). Such algorithms can be used to identify a material from many thousands of possible candidates. Screening algorithms evaluate whether at least a subset of features in an unknown measurement correspond to one or more specific substances of interest and are typically configured to detect from a small list potential target analytes. Thus, screening algorithms are much less broadly applicable than identification algorithms; however, they typically provide higher detection rates which makes them attractive for specific applications such as chemical warfare agent or narcotics detection. This paper will present an overview and performance characterization of a combined identification/screening algorithm that has recently been developed. It will be shown that the combined algorithm provides enhanced detection capability more typical of screening algorithms while maintaining a broad identification capability. Additionally, we will highlight how this approach can enable users to incorporate situational awareness during a response.

Laser induced breakdown spectroscopy is an attractive and versatile spectroscopic technique employed successfully for the detection of hazardous substances. The specific advantages of using femtosecond (fs) pulses with LIBS technique include lower ablation threshold, reduced background Continuum emission. In addition to atomic peaks in plasma the molecular peaks (CN and C₂) also play a significant role in classification of these samples. In the present work fs LIBS spectra were recorded from five different samples (RDX, HMX, NTO, ANTA, and DADNE) made in the form of pure pellets. Correlation statistics were used to discriminate the samples based on molecular, atomic ratios. This paper discusses, in detail, a simple correlation technique applied for the fs LIBS data for achieving classification.

Radiation in the Terahertz frequency range interacts with vibrations in the weakest molecular couplings such as hydrogen bonding, van der Waals forces, and hydrophobic interactions. The work presented demonstrates our efforts towards the development of a microfluidic device as the sample cell for presenting liquid samples within the detection region of a novel sub-THz spectrometer. The continuous-wave, frequency-domain spectrometer, operating at room temperature between 315 and 480 GHz with spectral resolution of 0.3 GHz, already demonstrated highly intense and specific signatures from nanogram samples of dry biological molecules and whole bacterial cells. The very low absorption by water in this sample cell will allow for the use of liquid samples to present cells and molecules in their natural environment. The microfluidic device design utilizes a set of channels formed with metal sidewalls to enhance the interaction between the THz radiation and the sample, increasing the sensitivity of the system. Combined with near field effects, through use of a detection probe close to the surface of the sample cell, spatial resolution less than the diffraction limit can be achieved, further reducing the amount of sample required for analysis. This work focuses on the design, and fabrication methods, which will allow implementation of the microfluidic sample cell device within the THz spectrometer. The device will be utilized for characterization of different cell types, showing that THz interrogation of liquid samples is possible.

Structural analysis via spectroscopic measurement of rotational and vibrational modes is of increasing interest for many applications, since these spectra can reveal unique and important structural and behavioral information about a wide range of materials. However these modes correspond to very low frequency (~5cm^-1 - 200cm^-1, or 150 GHz-6 THz) emissions, which have been traditionally difficult and/or expensive to access through conventional Raman and Terahertz spectroscopy techniques. We report on a new, inexpensive, and highly efficient approach to gathering ultra-low-frequency Stokes and anti-Stokes Raman spectra (referred to as “THz-Raman”) on a broad range of materials, opening potential new applications and analytical tools for chemical and trace detection, identification, and forensics analysis. Results are presented on explosives, pharmaceuticals, and common elements that show strong THz-Raman spectra, leading to clear discrimination of polymorphs, and improved sensitivity and reliability for chemical identification.

We previously reported the use of hollow metal and dielectric lined waveguides as gas cells used in real-time Raman spectroscopy of gas mixtures. Our team has constructed a multi-gas Raman sensor system capable of measuring molecular components in most gas mixtures with sub-percent accuracy and a sub-second sampling rate. This combination of speed and accuracy is enabled by the novel combination of optimized sample-cell collection and appropriate gas-stream configuration. Here, we discuss the new state-of-the-art in Raman process-gas analysis and share relevant testing data on our optimized system for potential industrial end-users. We conclude that a paradigm shift in technology for gas measurement applications could result from the instrumentation developed herein.

Many compact, portable Raman spectrometers have entered the market in the past few years with applications in narcotics and hazardous material identification, as well as verification applications in pharmaceuticals and security screening. Often, the required compact form-factor has forced designers to sacrifice throughput and sensitivity for portability and low-cost. We will show that a volume phase holographic (VPH)-based spectrometer design can achieve superior throughput and thus sensitivity over conventional Czerny-Turner reflective designs. We will look in depth at the factors influencing throughput and sensitivity and illustrate specific VPH-based spectrometer examples that highlight these design principles.

We are developing a novel approach for cleaning and confirming contaminated metallic surfaces that is based on laser ablation to clean the surfaces followed closely in time and space by laser analysis of the degree of cleanliness. Laser-based surface cleaning is a well-established technology and is commercially available (e.g., Adapt-Laser). The new development involves the integration of a LIBS (Laser Induced Breakdown Spectroscopy) surface analytical capability to analyze the surface before and right after the laser cleaning step for the presence or absence of unwanted residues. This all-laser approach is being applied to surfaces of steel vessels that have been used for the containment and destruction of chemical munitions. Various processes used for the destruction of chemical munitions result in the creation of oxidized steel surfaces containing residues (e.g., arsenic, mercury) that need to be removed to acceptable levels. In many instances inorganic molecular contaminants become integrated into oxide layers, necessitating complete removal of the oxide layer to achieve ideal levels of surface cleanliness. The focus of this study is on oxidized steel surfaces exposed to thermally decomposed Lewisite, and thus laden with arsenic. We demonstrate here that a commercially-available cleaning laser sufficiently removes the oxide coating and the targeted contaminants from the affected steel surface. Additionally, we demonstrate that LIBS is useful for the identification of arsenic and mercury on steel surfaces before and after laser cleaning, with arsenic being specifically tracked and analyzed at levels less than 1 microgram per square centimeter surface loading. Recent progress and future directions are presented and discussed.

The effect of finite beam extinction ratio on the precision and accuracy of cavity ring-down decay time constant measurements was examined using the frequency-agile, rapid scanning, cavity ring-down spectroscopy (FARS-CRDS) technique. This new approach to CRDS uses a waveguide-based electro-optic phase modulator (EOM) to provide a laser beam extinction ratio as high as 80 dB: a value that is ≈30 dB greater than that typically achieved with acousto-optic-modulator- based beam switches. We find that the observed measurement precision scales inversely with extinction ratio, such that an EOM enables measurement of the cavity ring-down decay time with a relative precision of ≈8×10^-5. We demonstrate that insufficient extinction can be the dominant cause of statistical uncertainty for extinction ratios below 60 dB. Furthermore, insufficient extinction can result in non-exponential decays, which cause systematic measurement biases in cavity losses and absorption.

There continues to be a need for improved technology to be used in theater to quickly and accurately identify the person who shot any weapon during a terrorist attack as well as to link a suspect to the actual weapon fired during a crime. Beyond this, in areas of conflict it would be desirable to have the capability to establish the source country for weaponry and ammunition. Gunshot residue (GSR) analysis is a reasonably well-studied technology area. Recent scientific publications have reported that the residues have a rich composition of both organic and inorganic compounds. For the purposes of identifying the manufacturer or country of origin for the ammunition, the inorganic components of GSR appear to be especially promising since their presence in the propellant and primer formulations are either specific to a given chemical formula, or they represent impurities in the manufacturing process that can be unique to a manufacturer or the source country for the chemicals used for propellants and primers. The Laser Induced Breakdown Spectroscopy (LIBS) technology has already demonstrated considerable capability for elemental fingerprinting, especially for inorganic/metallic components. A number of reports have demonstrated LIBS capability in forensics for matching materials such as inks, fabrics, paper, glass, and paint. This work describes the encouraging results of an initial study to assess a new commercial field-portable (battery operated) LIBS system for GSR analysis with gunshot residues having been collected from inside cartridge casings from 3 different ammunition manufacturers.

There is a need in many industries and government functions to identify the source of origin for various materials. For example, the food industry needs to ensure that the claimed source of some of the food products (e.g. coffee, spices) are in fact legitimate due to the variation of quality from different source locations world-wide. Another example is to identify the source country for imported commodities going through Customs so as to assess the correct tariff which varies depending on the source country. Laser Induced Breakdown Spectroscopy (LIBS) holds promise for being a field-portable tool for rapid identification of the country of origin of various materials. Recent research at Towson University has identified the elemental markers needed for discrimination of select spices back to their country of origin using wavelength dispersive X-ray fluorescence (WDXRF). The WDXRF device, however, is not particularly suitable for convenient and fast field analysis. We are extending this study to evaluate the potential of a benchtop commercial LIBS device that could be located at ports of entry and to compare its performance with WDXRF. Our initial study on the spice cumin has demonstrated that discriminant function models can not only be created with 100% separation between the 4 countries of origin (China, India, Syria, and Turkey), but also when tested they show 100% correct matching to the country of origin. This study adds to the growing number of publications that indicate the power of LIBS elemental fingerprinting for provenance determinations.

“Small” spectrometers fall into three broad classes: small versions of laboratory instruments, providing data, subsequently processed on a PC; dedicated analyzers, providing actionable information to an individual operator; and process analyzers, providing quantitative or semi-quantitative information to a process controller. The emphasis of this paper is on handheld dedicated analyzers. Many spectrometers have historically been large, possible fragile, expensive and complicated to use. The challenge over the last dozen years, as instruments have moved into the field, has been to make spectrometers smaller, affordable, rugged, easy-to-use, but most of all capable of delivering actionable results. Actionable results can dramatically improve the efficiency of a testing process and transform the way business is done. There are several keys to this handheld spectrometer revolution. Consumer electronics has given us powerful mobile platforms, compact batteries, clearly visible displays, new user interfaces, etc., while telecomm has revolutionized miniature optics, sources and detectors. While these technologies enable miniature spectrometers themselves, actionable information has demanded the development of rugged algorithms for material confirmation, unknown identification, mixture analysis and detection of suspicious materials in unknown matrices. These algorithms are far more sophisticated than the ‘correlation’ or ‘dot-product’ methods commonly used in benchtop instruments. Finally, continuing consumer electronics advances now enable many more technologies to be incorporated into handheld spectrometers, including Bluetooth, wireless, WiFi, GPS, cameras and bar code readers, and the continued size shrinkage of spectrometer ‘engines’ leads to the prospect of dual technology or ‘hyphenated’ handheld instruments.

Traditionally, samples are collected on-site (i.e., in the field) and are shipped to a lab for chemical analysis. An alternative is offered by using portable chemical analysis instruments that can be used on-site (i.e., in the field). Many analytical measurements by optical emission spectrometry require use of light-sources and of spectral lines that are in the Ultra-Violet (UV, ~200 nm – 400 nm wavelength) region of the spectrum. For such measurements, a portable, battery-operated, fiber-optic spectrometer equipped with an un-cooled, linear, solid-state detector may be used. To take full advantage of the advanced measurement capabilities offered by state-of-the-art solid-state detectors, cooling of the detector is required. But cooling and other thermal management hamper portability and use on-site because they add size and weight and they increase electrical power requirements. To address these considerations, an alternative was implemented, as described here. Specifically, a microfabricated solid-state detector for measurement of UV photons will be described. Unlike solid-state detectors developed on crystalline Silicon, this miniaturized and low-cost detector utilizes amorphous Selenium (a-Se) as its photosensitive material. Due to its low dark current, this detector does not require cooling, thus it is better suited for portable use and for chemical measurements on-site. In this paper, a microplasma will be used as a light-source of UV photons for the a-Se detector. For example, spectra acquired using a microplasma as a light-source will be compared with those obtained with a portable, fiber-optic spectrometer equipped with a Si-based 2080-element detector. And, analytical performance obtained by introducing ng-amounts of analytes into the microplasma will be described.

ThermoFisher Scientific (formerly Ahura Scientific) has developed a handheld, modular detection and identification system for trace-level gases, chemical vapors and aerosols, and swab analyses. The sample chamber is a separate, removable module that can be tailored specifically to the users’ needs. The vapor module can operate in three modes: ambient sampling, vapor/aerosol preconcentration, and direct injection. A swab module can be used to analyze thermally desorbed vapors from a sample swab. Limits of identification for vapors are as low as 0.1 ppm following a 15-min preconcentration period. The swab module can detect as little as 5 μg of TNT.

FT-IR spectroscopy is the technology of choice to identify solid and liquid phase unknown samples. The challenging ConOps 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, extreme reliability, 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 HazMatID™ Elite, a FT-IR instrument designed to balance the portability advantages of a handheld device with the performance challenges associated with miniaturization. In this paper, special focus will be given to the HazMatID Elite’s sampling interfaces optimized to collect and interrogate different types of samples: accumulated material using the on-board ATR press, dispersed powders using the ClearSampler™ tool, and the touch-to-sample sensor for direct liquid sampling. The application of the novel sample swipe accessory (ClearSampler) to collect material from surfaces will be discussed in some detail. The accessory was tested and evaluated for the detection of explosive residues before and after detonation. Experimental results derived from these investigations will be described in an effort to outline the advantages of this technology over existing sampling methods.

Lab-on-a-chip and optofluidic micro-systems often rely on bulky off-chip optical components such as lenses and spectrometers for detection. There is a growing demand for compact microspectrometers that can be integrated on-chip, to increase portability and potentially reduce the cost and complexity of these systems. We have previously reported chip-scale microspectrometers based on tapered air-core Bragg waveguides with omnidirectional Bragg claddings. Here, we describe the integration of these air-core waveguide spectrometers with microfluidics, including results for a prototype sensing system based on spectrally-resolved fluorescence detection.

Fourier-transform imaging systems can rapidly provide a great deal of information in a scene. Many applications require systems with no moving parts. One proposed approach uses birefringent crystal stages interspersed with liquid crystal cells acting as achromatic polarization rotators. Previous research has revealed that this system may have limited applicability because of severe limitations of the field-of-view for systems with large OPD. We provide a more in-depth analysis of these limitations using mostly Extended Jones Matrix simulations. We also propose a design modifications which greatly improves FOV, allowing higher resolutions to be achieved.

Low noise upconversion of IR images by three-wave mixing, can be performed with high efficiency when mixing the object radiation with a powerful laser field inside a highly non-linear crystal such as periodically poled Lithium Niobate. Since IR cameras are expensive and have high levels of intrinsic noise, we suggest to convert the wavelength from the mid infrared to the visible/NIR wavelength for simple detection using CCD cameras. The intrinsic noise in cameras has two main contributions. First, read noise originating from the charge to signal read-out electronics. This noise source is usually measured in number of electrons. The second noise source is usually referred to as dark noise, which is the background signal generated over time. Dark noise is usually measured in electrons per pixel per second. For silicon cameras certain models like EM-CCD have close to zero read noise, whereas high-end IR cameras have read noise of hundreds of electrons. The dark noise for infrared cameras based on semiconductor materials is also substantially higher than for silicon cameras, typical values being millions of electrons per pixel per second for cryogenically cooled cameras whereas peltier cooled CCD cameras have dark noise measured in fractions of electrons per pixel per second. An ideal solution thus suggest the combination of an efficient low noise image wavelength conversion system combined with low noise silicon based cameras for low noise imaging in the IR region. We discuss image upconversion as a means to do low noise conversion of IR light to visible light. We demonstrate system noise performance orders of magnitude lower than existing cryogenic cooled IR cameras.

A tunable waveguide-based frequency up-conversion detector is used for single photon level near infrared (IR) spectroscopic measurements. Applications include direct spectroscopic measurement of week near IR signals and remote bi-photon spectroscopy. We have demonstrated direct spectroscopy of single photon near IR signals from a greatly attenuated laser and a single photon source. We further applied the up-conversion spectrometer for frequency correlated bi-photon spectroscopy using a single photon source of non-degenerate photon pairs at 1310 nm (near IR) and 895 nm. In correlated bi-photon spectroscopy, the spectral function at one wavelength range of a remote object can be reproduced by locally measuring another (near IR) wavelength range using the up-conversion spectrometer and monitoring the coincidence counts. A near IR single photon detection efficiency of 32 % has been achieved with the up-conversion spectrometer. The spectral resolution of the system is approximately 0.2 nm at 1310 nm based on the acceptance width of the up-conversion chip used. In bi-photon spectroscopy, the spectral resolution for the correlated photons at 895 nm is approximately 0.1 nm. The sensitivity achieved using the up-conversion detector is -126 dBm at 1310 nm.

We report on our current status towards the development of a prototype Fourier transform infrared phase shift cavity ring down spectrometer (FTIR-PS-CRDS) system under a U.S. EPA SBIR contract. Our system uses the inherent wavelength-dependent modulation imposed by the FTIR on a broadband thermal source for the phase shift measurement. This spectrally-dependent phase shift is proportional to the spectrally-dependent ring down time, which is proportional to the losses of the cavity including those due to molecular absorption. Our approach is a broadband and spectral range enhancement to conventional CRDS which is typically done in the near IR at a single wavelength; at the same time our approach is a sensitivity enhancement to traditional FTIR owing to the long effective path of the resonant cavity. In this paper we present a summary of the theory including performance projections and the design details of the prototype FTIR-PS-CRDS system.

A millimeter-wave spectroscope for the detection of triatomic gases has been constructed and characterized for frequencies between 230 and 325 GHz (H-band). The achieved results demonstrate a high sensitivity and low threshold detection. A circular lensed horn antenna transmits millimeter- waves into a gas-filled vacuum tube and excites triatomic gas molecules to a higher energy level, if the rotational resonance frequency of the molecule matches with the excitation frequency. At the other end of the tube a second lensed horn antenna receives the propagated electromagnetic wave and the millimeter-wave power is measured by a heterodyne receiver. By sweeping the radiated transmit frequency, the molecules' specific absorption can be detected. The measured absorption results are superimposed by standing wave effects within the tube. To eliminate the standing wave effects, spectroscopy on the basis of rotational spontaneous millimeter-wave emission was examined. This kind of spectroscopy decouples the transmitted from the received signal, whereby independent excitation and detection of the molecules are realized. The use of additional absorbers at the end of the gas tube decreases the decay time of the radiated wave inside the gas cell. In this paper, the detection of spontaneous emission of triatomic gas molecules with the use of a pulse-controlled transmitter and receiver is shown. Optimizations improved the stability and reproducibility of the measurements, and the detection threshold of nitrous oxide could be decreased to a ratio of 1/400. Furthermore, the implementation of a differential measurement method reduces the measurement time by a factor of 150 and simultaneously decouples of environmental influences.