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Raman hyperspectral imaging (RHSI) is an emerging chemical imaging technique that provides spectral and spatial information simultaneously in one measurement, and therefore can be a valuable tool for the detection and analysis of targets located in complex backgrounds. In particular, RHSI is useful for the detection and identification of threat materials (i.e., homemade and military-grade explosives) on the surfaces, where the concentration of target of interest could be very low and is typically found within complex scenery. Raman spectroscopy has the capability to provide a distinct molecular fingerprint of a threat material for unambiguous identification, can work at standoff distances (up to 100+ meters), and is capable of being conducted remotely, which makes it beneficial for installation into a stationary vehicle screening assembly. In spite of its numerous advantages, the implementation of Raman instrumentation for hyperspectral imaging is rather challenging owing to the low Raman scattering efficiency, potentially high SWaP constraints, and the need for a tightly focused laser spot that may result into the photo or thermal degradation of the sample. Some limitations can be overcome by utilizing the deep UV laser excitation, as the Raman cross section increases exponentially, i.e., ν4 with laser frequency. However, current generation UV Raman spectrometers require very narrow slit widths and long focal length optics, which means they have very low optical throughput, can be physically large and heavy, and can only probe an area the size of a tightly focused laser beam, eliminating the option to investigate large areas with defocused excitation. In addition, the use of focused laser excitation creates eye-safety concerns that restricts the usage of Raman sensors for most real-world applications To address these issues, ChemImage Sensor Systems (CISS) is developing a hyperspectral Raman imaging system capable of yielding high spectral resolution in a small form factor while using eye-safe, defocused laser excitation. This innovation combines a spatial heterodyne spectrometer (SHS), a slit-less spectrometer that operates similar to Michelson interferometer without requiring moving parts, with a fiber array spectral translator (FAST) fiber array, a twodimensional imaging fiber that provides spatial information of the target area. This combination of technologies, known as FAST-SHS that is compatible with deep UV excitation and creates a high throughput Raman hyperspectral imager capable of yielding very high spectral resolution measurements while simultaneously providing expanded area coverage and a faster search rate than traditional Raman systems. Recently, we have developed a FAST-SHS system consisting of fiber bundles with numerous fibers. FAST-SHS is the first spatial heterodyne Raman spectrometer to incorporate FAST technique that is capable of performing hyperspectral measurements at various standoff distances using defocused laser excitation. This paper will discuss the background of FAST-SHS technology for Raman hyperspectral imaging, the initial setup and design of the sensor, and provide initial detection results for wide area detection capabilities for the identification and analysis of threat targets.

Raman hyperspectral imaging (HSI) is a valuable technique for the detection of threat materials (i.e. explosives and/or narcotics), especially if those materials are located in a complex area with varied background constituents. Raman spectroscopy can provide a unique molecular fingerprint of a threat material, which allows it to provide near unambiguous threat identification. Unfortunately, the current generation of Raman sensors have numerous limitations that hinder their performance and limit their ability to be applied in real world scenarios. These limitations include low optical throughput, larger size/weight requirements, and area of interrogation size limited to the size of a focused laser spot. These limits are typically due to a system’s spectrometer, commonly a dispersive grating based approach that requires a narrow entrance slit width and long focal length optics to accurately resolve and pass the collected scattered light onto the detector. In addition, using focused laser excitation creates eye-safety concerns that can restrict the usage of Raman sensors for most real-world applications. To address these issues, ChemImage Corporation is developing a next generation Raman sensor capable of providing a wide-area of coverage and improved eye-safety using defocused laser excitation. This is made possible by utilizing a spatial heterodyne spectrometer (SHS), a slit-less grating-based Michelson interferometer with no moving parts. The entrance aperture to the SHS can be orders of magnitude larger than a traditional spectrometer’s entrance slit, which provides an etendue gain of equal magnitude. This feature also allows the laser to be utilized in a defocused configuration, providing an area of coverage up to centimeters in diameter. The sensor also comprises a fiber-array spectral translator (FAST) bundle, a 2-D hyperspectral imaging fiber composed of dozens of smaller fibers, which gives the sensor the ability to spatially discriminate the area of interrogation. The combination of these two technologies is termed FAST-SHS. This paper will provide the background of spatial heterodyne spectroscopy and Raman hyperspectral imaging, the setup and design of a breadboard FAST-SHS, and provide initial results.

Raman hyperspectral imaging (HSI) can be an advantageous technique for the detection and identification of threat materials (i.e. homemade and military grade explosives), especially if those materials are located in a complex scene. Raman spectroscopy has the capability to provide a distinct molecular fingerprint of a threat material, which gives it the ability to provide near unambiguous threat identification. Unfortunately, the current generation of Raman sensors have numerous limitations that hinder their performance and limit their ability to be applied in real world scenarios. These systems offer low optical throughput, have larger size/weight requirements, and can only interrogate an area of interest the size of a focused laser spot. These limitations are typically due to a system’s spectrometer, which traditionally utilizes a dispersive grating and requires a narrow entrance slit width and long focal length optics to accurately accept and pass the collected scattered light onto the detector. In addition, the use of focused laser excitation creates eye-safety concerns that restrict the usage of Raman sensors for most real-world applications. With these issues in mind, ChemImage Sensor Systems (CISS) is developing a next generation Raman sensor capable of providing a wide-area of coverage and improved eye-safety using defocused laser excitation. This is made possible by utilizing a spatial heterodyne spectrometer (SHS), a slitless grating-based Michelson interferometer with no moving parts. The entrance aperture to the SHS can be centimeters in diameter, which provides the SHS an etendue orders of magnitude greater than a traditional spectrometer. This feature also allows the excitation laser to be defocused to centimeters in diameter. In addition, the sensor utilizes a fiber-array spectral translator (FAST) bundle, a 2-D hyperspectral imaging fiber composed of hundreds of smaller fibers, which gives the sensor the ability to spatially distinguish the area of interrogation. The combination of these two technologies is termed FAST-SHS. This paper will discuss the background of spatial heterodyne spectroscopy and Raman hyperspectral imaging, the initial setup and design of the sensor, and provide initial detection results.

This study was conducted to evaluate the feasibility of using Raman chemical imaging (i.e., Raman imaging microspectroscopy) to establish chemical identity, particle size and particle size distribution (PSD) for a representative corticosteroid in aqueous nasal spray suspension formulations.The Raman imaging PSD protocol was validated using polystyrene (PS) microsphere size standards (NIST-traceable). A Raman spectral library was developed for the active and inactive compounds in the formulation. Four nasal sprays formulated with beclomethasone dipropionate (BDP) ranging in size from 1.4 to 8.3 microm were imaged by both Raman and brightfield techniques. The Raman images were then processed to calculate the PSD for each formulation.Within each region examined, active pharmaceutical ingredient (API) particles are unambiguously identified and the total number of those particles, particle size and PSD of API free of excipients and PSD of API particles adhered to other excipients are reported.Good statistical agreement is obtained between the reported and measured sizes of the PS microspheres. BDP particles were clearly distinguishable from those of excipients. Raman chemical imaging (RCI) is able to differentiate between and identify the chemical makeup of multiple components in complex BDP sample and placebo mixtures. The Raman chemical imaging method (coupled Raman and optical imaging) shows promise as a method for characterizing particle size and shape of corticosteroid in aqueous nasal spray suspension formulations. However, rigorous validation of RCI for PSD analysis is incomplete and requires additional research effort. Some specific areas of concern are discussed.

Raman spectroscopy is a valuable tool for the investigation and analysis of explosive and biological analytes because it provides a unique molecular fingerprint that allows for unambiguous target identification. Raman can be advantageous when utilized with deep UV excitation, but typical deep UV Raman systems have numerous limitations that hinder their performance and make their potential integration onto a field portable platform difficult. These systems typically offer very low throughput, are physically large and heavy, and can only probe an area the size of a tightly focused laser, severely diminishing the ability of the system to investigate large areas efficiently. The majority of these limitations are directly related to a system’s spectrometer, which is typically dispersive grating based and requires a very narrow slit width and long focal length optics to achieve high spectral resolution. To address these shortcomings, ChemImage Sensor Systems (CISS), teaming with the University of South Carolina, are developing a revolutionary wide-field Raman hyperspectral imaging system capable of providing wide-area, high resolution measurements with greatly increased throughput in a small form factor, which would revolutionize the way Raman is conducted and applied. The innovation couples a spatial heterodyne spectrometer (SHS), a novel slit-less spectrometer that operates similar to Michelson interferometer, with a fiber array spectral translator (FAST) fiber array, a two-dimensional imaging fiber for hyperspectral imagery. This combination of technologies creates a novel wide-field, high throughput Raman hyperspectral imager capable of yielding very high spectral resolution measurements using defocused excitation, giving the system a greater area coverage and faster search rate than traditional Raman systems. This paper will focus on the need for an innovative UV Raman system, provide an overview of spatial heterodyne Raman spectroscopy, and discuss the development of the system.

Identification of thaumasite (CaSiO3·CaO3·CaSO4·15H2O) in concrete undergoing external sulfate attack by X-ray powder diffraction or by microscopic techniques is difficult due to its crystallographic and morphological similarity with ettringite. Widefield Raman chemical imaging via liquid crystal tunable filter (LCTF) technology has been used in a preliminary study to determine the presence of thaumasite in association with ettringite (3CaO·Al2O3·3CaSO4·32H2O) and gypsum (CaSO4·2H2O). Raman chemical imaging combines Raman spectroscopy with optical microscopy and digital imaging to provide images with molecular-based contrast. Thaumasite has three major peaks at 658, 990, 1076 cm−1 and three minor peaks at 417, 453, 479 cm−1. Ettringite has major peaks at 990, 1088 cm−1. Gypsum has a major peak at 1009 cm−1 and minor peaks at 417, 496, 621, 673, 1137 cm−1. When these minerals are presented together, Raman chemical imaging provides an excellent way to determine their molecular composition and spatial distribution within the sample.

A dimension reduction fiber-optic array is used to measure the response of a stacked-layer, image-guide CO2/O2 sensor, simultaneously at several different wavelengths. Two different image-guide CO2/O2 sensor configurations are described: a stacked-layer sensor, where luminescence indicators for CO2 and O2 are uniformly coated on the tip of the sensor; and a side-by-side coated sensor where the two indicators are coated on different halves of the fiber tip. It is shown that a single image-guide measurement, made by using the dimension reduction array, can be used to generate response plots, intensity profiles, and reconstructed images at different luminescence wavelengths. The spatial resolution of an image guide sensor is limited by the number of fibers used to construct the dimension reduction array.

A single-frame approach to chemical imaging with high spectroscopic resolution is described that makes use of a second-generation dimension-reduction fiber-optic array. Laser-induced plume images are focused onto a 17 × 32 rectangular array of square close-packed 25 μm cross-sectional f/2 optical fibers that are drawn into a 544 × 1 distal array with serpentine ordering. The 544 × 1 side of the array is imaged with an f/2 spectrograph equipped with a holographic grating and a gated intensified charge-coupled device (ICCD) camera for spectral analysis. Software is used to extract the spatial/spectral information contained in the ICCD images and de-convolute them into wavelength-specific univariate reconstructed images or position-specific spectra that span an 86 nm wavelength space. Temporal resolution is provided by imaging sequential laser plumes with varying time delays after each laser pulse on the gated intensifier.

A novel system for rapid chemical imaging is described and evaluated. The system operates via single-frame spectroscopic chemical imaging with high spectroscopic resolution using a second-generation dimension-reduction fiberoptic array. Images are focused onto a rectangular array of square close-packed 25 μm cross-sectional f/2 optical fibers that are drawn into a linear distal array with serpentine ordering. The distal end is then imaged with an f/2 spectrograph equipped with a holographic grating and a gated intensified charge-coupled device (ICCD) camera for analysis. Software is used to extract the spatial/spectral information contained in a single ICCD image and deconvolute it into wavelength-specific univariate reconstructed images or position-specific spectra that span an 86 nm wavelength space using our present grating. A description of the fabrication of the dimension-reduction array is given as well as a zero-order reconstruction of a binary target and single-wavelength image reconstructions of ...

Optical standoff detection of hazardous materials has been developed that combines hyperspectral IR imaging, Raman imaging and laser induced breakdown spectroscopy. Sensor characteristics will be presented.

A novel sensor concept for optical standoff detection of explosives that combines Raman hyperspectral imaging and laser induced breakdown spectroscopy (LIBS) is described. Conceptually, the standoff optical sensor trades off the high sensitivity of LIBS elemental analysis with the high specificity of Raman molecular analysis to provide, overall, a high sensitivity, low false alarm rate standoff identification strategy for explosives on surfaces. In this paper, Raman hyperspectral imaging results are presented in an initial assessment of the standoff Raman detection performance.

Liquid crystal tunable filters (LCTF) have been used in systems developed for Raman Chemical Imaging spectroscopy of chemical, biological and explosives threat materials. However, an ongoing challenge in detecting trace levels of materials is the limited throughput provided by previous generation LCTFs. In this article, we describe a new class of birefringent LCTFs based on a Multi-Conjugate Filter design that provides high throughput over an extended wavelength range (440 nm-750 nm). The spectral resolution, tuning accuracy, out-of-band rejection efficiency have been evaluated and are demonstrated on a Raman chemical imaging microscope platform. Detection of trace threat particulate matter in the presence of complex background with improved overall detection performance is demonstrated.

Plotting defect locations in insulating SiC presents a challenge because the total number of locations on a wafer is so large. We scan the wafer with visible light at an appropriate resolution and sort out transmissions appropriate for the defects we are looking for. Under these conditions, we find that voids and micropipes reduce the pixel transmission to 0.3 to 0.5. Sorting for this transmission reduces the number of pixels of interest to a manageable number, especially with recent progress in growing lower defect SiC. Now a commercial plotting program can easily display defect locations within a circle representing the wafer boundary. We verify the defect locations by scanning electron microscope secondary electron images and scanning optical microscope visible-light images at several resolutions.

Raman imaging instrumentation has advanced significantly since the first Raman images were obtained nearly three decades ago. Substantial improvements have been made in point scan, line scan, and widefield Raman imaging platform designs. The focus of this chapter is on Raman imaging instrumentation with respect to food science applications. Current technological approaches used in Raman imaging instrumentation, Raman instrumentation platform types, signal-enhanced Raman instrumentation, tandem Raman imaging instruments that benefit from orthogonal information obtained from multiple sensor types, and how to assess performance of a Raman imaging instrument are detailed with food science examples. Raman imaging instruments are the tools used to determine where molecular-specific Raman scatter arises in highly heterogeneous materials. These instruments are used to generate hundreds, thousands, or even millions of independent, spatially resolved Raman spectra from the material of interest. The resulting hyperspectral data cube consists of a series of wavelength-specific images where each pixel contains a Raman spectrum associated with the material imaged at that location. The Raman spectra in the hypercube are processed to reveal image contrast that is chemical specific without the need for stains, dyes, or contrast agents. Consequently, there is often a reduced burden or even no need for sample preparation unlike many other material analysis tools. Keywords: Raman chemical imaging; hyperspectral; foodstuffs; adulteration

As the demand for high quality, low cost X-ray, (gamma) -ray and imaging detector devices increases, there is a need to improve the quality and production yield of semiconductor materials used in these devices. One effective strategy for improving semiconductor device yield is through the use of better device characterization tools that can rapidly and nondestructively identify defects at early stages in the fabrication process. Early screening helps to elucidate the underlying causes of defects and to reduce downstream costs associated with processing defect laden materials that are ultimately scrapped. We report here a method for characterizing tellurium inclusion defects in cadmium zinc telluride semiconductor materials based on near infrared imaging. With this approach, large area wafers are inspected rapidly and non-destructively in two and three spatial dimensions by collecting NIR image frames at multiple regions of interest throughout the wafer using an automated NIR imaging system. The NIR image frames are subjected to image processing algorithms including background correction and image binarization. Particle analysis is performed on the binarized images to reveal tellurium inclusion statistics, sufficient to pass or fail wafers. In addition, data visualization software is used to view the tellurium inclusions in two and three spatial dimensions.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A dimension reduction technique is described that allows chemical images to be obtained using an image-guide sensor simultaneously at many different wavelengths with very high spectral resolution. Dimension reduction is accomplished using a custom 2D to 1D square fiber-optic array that is made by using approximately 600 individual 25 micron square fibers. The technique allows the concurrent detection of multiple analytes and is demonstrated using a combination CO 2 /O 2 sensor, in two different sensor configurations. The technique is being extended for lifetime-based image-guide sensors.

A single-frame approach to chemical imaging with high spectroscopic resolution is described that makes use of a second generation dimension-reduction fiber-optic array. Laser-induced plume images are focused onto a 17 x 32 rectangular array of square close-packed 25 p.m cross-sectionalfl2 optical fibers that are drawn into a 544 x 1 distal arraywith serpentine ordering. The 544 x 1 side of the array is imaged with an fl2 spectrograph equipped with a holographicgrating and a gated intensified charge-coupled device (ICCD) camera for spectral analysis. Software is used to extract thespatial/spectral information contained in the ICCD images and deconvolute them into wavelength-specific univariatereconstructed images or position-specific spectra that span an 86 nm wavelength space.Keywords: fiber-optics, chemical imaging, spectroscopic imaging, laser-induced breakdown spectroscopy (LIBS) 1. INTRODUCTION The proper spectroscopic interpretation of numerous industrial, medicinal, and biological samples requires an in

A novel optical approach to single-shot chemical imaging with high spectroscopic resolution is described using a prototype dimension-reduction fiber-optic array. Images are focused onto a 30 X 20 array of hexagonally packed 250- micrometers o.d. f/2 optical fibers which are drawn into a 600 X 1 distal array with specific ordering. The 600 X 1 side of the array is imaged with an f/2 spectrograph equipped with a holographic grating and a CCD images and deconvolute them into wavelength-specific reconstructed images or position-specific spectra which span a 190-nm wavelength space. 'White-light' zero-order images and first- order spectroscopic images of laser plumes have been reconstructed to illustrate proof-of-principle.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new optical computation method for the monitoring of chemical reactions requires filters with spectral transmittance curves that vary in a complicated way with wavelength. In this paper we consider the design of two different sets of filters, one of which could be used to predict the degree of curing of a polymer from an analysis of its Raman spectra. The problem is not easy because the required filters have sharp spectral features in a narrow spectral region. Two different design methods are used. The performance of one set designed by conventional means is very close to the specifications. However, current thin film deposition methods are probably incapable of producing filters of such thickness. The second solution is based on the use of several filters placed in series. It should be possible to implement this particular solution, but its performance is not nearly as good. Nevertheless, calculations indicate that this filter pair should also result in a satisfactory control of the curing process.

Electron irradiation during reflection high-energy electron diffraction is shown to affect the materials properties of ZnSe and GaN during growth by molecular beam epitaxy. The high-energy electrons produce an electron stimulated desorption effect during growth of ZnSe, which primarily affects adsorbed Se. Se desorption rates under electron irradiation are shown to be significantly larger than thermal desorption rates. Electron irradiation also decreases ZnSe growth rates under Zn-rich conditions. The decrease can be suppressed by either growth under Se-rich conditions or by using high index substrate orientations, in this case (211)B. Electron irradiation also influences growth rates for GaN grown by rf plasma-assisted molecular beam. Characterization using Raman and photoluminescence spectroscopy along with secondary ion mass spectrometry indicate electron irradiation can have a dramatic impact on point defect and impurity content of GaN.