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A compact SWIR/MWIR infrared hyperspectral imaging polarimeter (IHIP) is currently under development at the Optical Detection Lab at the University of Arizona. The sensor uses a pair of sapphire Wollaston prisms and high order retarders to form an imaging birefringent Fourier transform spectropolarimeter. Polarimetric data are acquired through the use of channeled spectropolarimetry to modulate the spectrum with the Stokes parameter information. The two dimensional interferogram is Fourier filtered and reconstructed to recover the complete Stokes vector data across the image. The IHIP operates over a +/-5° field of view and will use a dual-scan false signature reduction technique to suppress polarimetric aliasing artifacts. We present current instrument development progress, initial laboratory results, and our plan for future work.

The authors have previously called attention to the importance of atmospheric and aerosol emission in IR imaging device performance. The present paper derives a more precise and general result than the empirically derived expressions in the earlier paper. The same general conclusion, that atmospheric and aerosol emissions are an important factor in IR imaging performance, is supported, assuming that the system is photon noise-limited.

Gold-plated sandpaper was investigated for use as a Lambertian standard reference reflector for the IR spectrum. Various grit sizes from 3 to 400 microm and material types (i.e., silicon carbide and aluminum oxide) were studied. The different gold-plated sandpaper grit sizes were measured in the same way using three laser wavelengths (0.6328, 3.39, and 10.6 microm) at five angles of incidence of the source (0, 10, 20, 30, and 60 degrees ). All the scattering measurements were performed in the plane of incidence. The best choices of sandpaper grit sizes were 9-microm A1(2)O(3) for 0.6328- and 3.39-microm radiation and 600 grit by Armak Co. for 10.6-microm radiation. These choices were compared with other commonly used reflectors such as magnesium oxide, halon, sintered bronze, and flowers of sulfur. An attempt was made to correlate surface roughness (size of grit) to the degree of approximation to a good Lambertian reflector, but it was found that grit size is not as important as the filling factor, or density of particles, over a given area. It was found that fairly good approximations to Lambertian behavior result when the angle of incidence is small but not when the angle of incidence is as large as 60 degrees .

The theoretical and experimental demonstration of a dispersion-compensated polarization Sagnac interferometer (DCPSI) is presented. An application of the system is demonstrated by substituting the uniaxial crystal-based Savart plate (SP) in K. Oka's original snapshot polarimeter implementation with a DCPSI. The DCPSI enables the generation of an achromatic fringe field in white-light, yielding significantly more radiative throughput than the original quasi-monochromatic SP polarimeter. Additionally, this interferometric approach offers an alternative to the crystal SP, enabling the use of standard reflective or transmissive materials. Advantages are anticipated to be greatest in the thermal infrared, where uniaxial crystals are rare and the at-sensor radiance is often low when compared to the visible spectrum. First, the theoretical operating principles of the Savart plate polarimeter and a standard polarization Sagnac interferometer polarimeter are provided. This is followed by the theoretical and experimental development of the DCPSI, created through the use of two blazed diffraction gratings. Outdoor testing of the DCPSI is also performed, demonstrating the ability to detect either the S(2) and S(3), or the S(1) and S(2) Stokes parameters in white-light.

We have developed a staring‐mode, high‐speed infrared camera based on a RCA 160×244 PtSi Schottky‐barrier charge‐coupled device image sensor. The camera uses a unique method to achieve greater temporal resolution of rapidly varying thermal phenomena in the 3–5 μm band. Rather than increase the imager’s frame rate, we decrease the image integration time while maintaining a frame rate that is compatible with standard RS‐170 video. This technique allows us to display and record repetitive events that occur at frequencies up to 5 kHz with conventional video equipment. In this article we describe the theory and operation of this system.

A long wave infrared (LWIR) division of amplitude imaging Stokes polarimeter is presented. For the first time, to our knowledge, application of microbolometer focal plane array (FPA) technology to polarimetry is demonstrated. The sensor utilizes a wire-grid beamsplitter with imaging systems positioned at each output to analyze two orthogonal linear polarization states simultaneously. Combined with a form birefringent wave plate, the system is capable of snapshot imaging polarimetry in any one Stokes parameter (S1, S2 or S3). Radiometric and polarimetric calibration procedures for the instrument are provided and data from the instrument are presented, demonstrating the ability to measure intensity variations corresponding to polarized emission in natural environments. As such, emission polarimetry can be exploited at significantly reduced cost, sensor size and power consumption over instruments based on more costly Mercury-Cadmium Telluride (MCT) FPA's.

Channeled spectropolarimetry, first developed by K. Oka, is capable of measuring all the Stokes parameters from a single modulated spectrum. We present a theoretical means for improving the spectral resolution of channeled spectropolarimetry by at least a factor of four. Especially valuable in the infrar ed due to atmospheric absorption features, this method simultaneously provides for the correction of aliasing artifacts from the channels used for the determination of the Stokes parameters. The technique is experimentally demonstrated using a Fourier transform infrared spectrometer and two multiple-order Yttrium Vanadate (YVO 4 ) retarders. This approach is implem ented with consideration of crystal dichroism effects, and reconstructions are compared with conventional channeled spectropolarimetric reconstructions from the same system. Additional results, produced by using Cadmium Sulfide (CdS) retarders, provide demonstration of the technique across the infrared. Keywords: Spectropolarimeter, Fourier transf orm spectrometer, atmospheric absorption, channeled spectrum.

A complete Fourier Transform Spectropolarimeter in the MWIR is demonstrated. The channeled spectral technique, originally developed by K. Oka, is implemented with the use of two Yttrium Vanadate (YVO(4)) crystal retarders. A basic mathematical model for the system is presented, showing that all the Stokes parameters are directly present in the interferogram. Theoretical results are compared with real data from the system, an improved model is provided to simulate the effects of absorption within the crystal, and a modified calibration technique is introduced to account for this absorption. Lastly, effects due to interferometer instabilities on the reconstructions, including nonuniform sampling and interferograms translations, are investigated and techniques are employed to mitigate them.

A reconstructed hyperspectral datacube has been successfully recovered from a badly flawed point-spread function (PSF) observation. The corrected PSF alleviated unnoticed detector saturation and misregistration artifacts in the calibration of a crucial, irreplaceable near-infrared flash hyperspectral imager dataset. This flawed PSF induced a defocus-like artifact as well as spectral distortions in the three-dimensional hyperspectral estimate of the data. The PSF artifacts, which would have caused severe misinterpretation of the spatio-spectral information, were correctable post detection using an optical model of the PSF constrained by the available flawed calibration.

Channeled spectropolarimetry is a novel method of measuring the spectral and polarization content of light. It employs amplitude modulation to encode all four Stokes component spectra into a single optical power spectrum. We describe a practical approach to system calibration and object reconstruction, which is able to account for important non-ideal effects. These include dispersion in retarder materials and limited spectral resolution in the incorporated spectrometer. The spectropolarimeter is modeled as a linear operator, represented in practice by a matrix. The matrix is estimated in the calibration, and pseudoinverted subject to a constraint on object space for reconstructions. Experimental results are shown and compared with reference measurements. An example is given of the technique’s application to the characterization of time-varying, stress-induced birefringence.

The imaging polarimeter using the Savart plates is modified for use with the polychromatic light by incorporating an imaging system utilizing diffractive lenses. Its feasibility is numerical simulated for the visible light with 50nm-bandwidth.

This paper presents the results of a study of pecan spectral reflectances. It describes an experiment for measuring the contrast between several components of raw pecan product to be sorted. An analysis of the experimental data reveals high contrast ratios in the infrared spectrum, suggesting a potential improvement in sorting efficiency when separating pecan meat from shells. It is believed that this technique has the potential to dramatically improve the efficiency of current sorting machinery, and to reduce the cost of processing pecans for the consumer market.

We show that a fundamental upper limit of specific detectivity (D∗) exists for high-temperature superconducting thin-film quantum detectors biased at or above the critical current, Ic. This limit is a function of the inter-electrode length, the thickness of the film, and the critical current density rather than a function of the length-to-width aspect ratio. For typical film parameters, a maximum value of D∗ is 6.3 × 10 10 cm-Hz 1 2 /W .

Computed tomographic imaging spectrometers measure the spectrally resolved image of an object scene in an entirely different manner from traditional whisk-broom or push-broom systems, and thus their noise behavior and data artifacts are unfamiliar. We review computed tomographic imaging spectrometry (CTIS) measurement systems and analyze their performance, with the aim of providing a vocabulary for discussing resolution in CTIS instruments, by illustrating the artifacts present in their reconstructed data and contributing a rule-of-thumb measure of their spectral resolution. We also show how the data reconstruction speed can be improved, at no cost in reconstruction quality, by ignoring redundant projections within the measured raw images.

Optics has recently evolved into one of the most flourishing fields in physics, with photonics finding increasing application in products such as optical thermometers, camera monitors and LED lighting, plus numerous military applications. This book covers the geometrical aspects of optics, the fundamental level of understanding the technology. Beginning with how light is generated and how fast it travels, the book discusses how materials interact with light, how various materials affect the velocity of light, and the ramifications of change in the speed of light. The concept of the index of refraction, and how it is used with Snell's law to produce image forming systems, is developed. An ideal textbook for advanced undergraduate level courses in geometrical optics, this book will also interest those wanting to learn the concepts and theory of geometrical optics. Each chapter contains worked examples, and there are exercises to reinforce the reader's understanding of material.

Our tour through paraxial optics has only considered perfect images of scenes in which a point source in object space was mapped to a point in image space using paraxial rays. Gaussian optics also produced perfect images outside the paraxial region. Paraxial optics, however, is only a first-order approximation to a real optical system. Realizable optical systems do not produce perfect point images from point sources (represented mathematically as a delta function). In real optical systems, there is some blur or spreading of the point image. Diffraction The complex propagation of light passing through an aperture stop of a lens system will form a less than perfect image (for a detailed explanation of Huygens' wavefronts and propagation see Mahajan (2001)). In fact, the best one can do is to make the system “diffraction-limited.” Diffraction occurs when a wavefront (radiant beam) impinges upon the edge of an opaque screen or aperture. Light appears outside the perfect geometrical shadow because the light has been diffracted by the edge of the aperture. The effect this has on our simple rotationally symmetric optical systems is that a point does not map to a point, but is blurred or smeared. You may have observed the effect of the diffraction of light from a portal where there is light beyond what would be defined as the geometrical shadow boundary. If a wavefront, as shown in Figure 11.1, passes through a circular aperture, it does not continue as a circular disc.

There are certain classes of astronomical objects that have rather involved spectra that can also be a composite of a number of different spectral signatures, as well as spatial characteristics that can be used for identification and analysis. Such objects include galaxies and quasars with active nuclei, colliding / interacting galaxies, and globular cluster systems around our own Milky Way and other galaxies. Flash hyperspectral imaging adds coherence-time limited functionality so that Earth orbiting spacecraft and solar system objects such as planets, asteroids and comets can be spectrally imaged as well, as these also have both spatial and spectral structure rotating and moving within much shorter time spans. Flash hyperspectral imaging systems are, therefore, also useful for faster simultaneous spatial and spectral feature analysis. Previous work has explored spectral unmixing and other types of feature extraction of these general types of objects, but without consideration of the hyperspectral imaging system involved, neither in how the data is collected nor in how the datacube is reconstructed. We will present a proof of concept simulation of a resolved object as it is imaged through such a physically modeled imaging system and its datacube reconstructed. Finally, we provide a demonstration of the capability with astronomical data, Venus and a binary star, when constrained by our physical model of the instrumental transfer function.

A computed tomographic imaging spectrometer (CTIS) is an instrument which can simultaneously obtain image spatial and spectral information without moving parts in a single focal plane array integration time. When this instrument is combined with a channeled spectropolarimeter, the instrument can also obtain complete Stokes polarization information at each resolution element. The combined instrument, called a computed tomographic imaging channeled spectropolarimeter (CTICS), has been developed in the visible wavelength region. This paper summarizes the CTICS design and results obtained from data acquired during field testing of the CTICS instrument.

This paper will describe methods of measuring all of the components of the Stokes polarization vector for each pixel in a scene using only one frame of passive optical sensor data, one radar pulse, or one radiometer integration interval. Both active and passive sensors operating in any waveband from microwave to visible will be considered. For systems operating in the millimeter wave and terahertz bands, the techniques developed by Dereniak and his students at the University of Arizona will be discussed. For other wavebands, a technique developed by the author that requires the coherent reception of two orthogonally-polarized signal components will be presented. This latter method works for both for both broad-band and narrow-band active or passive signals, but requires focal planes and hardware in the visible and infrared bands that may be too complicated for many applications. Results of calculations made for the millimeter and terahertz bands will be presented.

Two imaging systems have been designed and built to function as snapshot imaging spectropolarimeters; one system made to operate in the visible part of the spectrum, the other for the long wavelength infrared, 8 to 12 microns. The devices are based on computed tomographic imaging channeled spectropolarimetry (CTICS), a unique technology that allows both the spectra and the polarization state for all of the wavelength bands in the spectra to be simultaneously recorded from every spatial position in an image with a single integration period of the imaging system. The devices contain no moving parts and require no scanning, allowing them to acquire data without the artifacts normally associated with scanning spectropolarimeters. Details of the two imaging systems will be presented.

A 2-Cam micro-bolometer imaging polarimeter operating in the LWIR is presented. The system is capable of snapshot imaging Stokes polarimetry in any one channel (S1, S2, or S3) by taking two simultaneous measurements of a scene. For measurements of S1 or S2, the instrument relies on a specially optimized wire-grid beam-splitter. For measurements of S3, a form birefringent quarter-wave retarder is inserted into the optical path. Specifics associated with the design of the wire-grid beam-splitter and the form birefringent quarter-wave retarder will be overviewed, with inclusion of RCWA simulations. Calibration and simulation procedures, as well as calibration targets, will be highlighted, and initial data from the instrument are presented.

We report results from a demonstration of a midwave-infrared non-scanning, high speed imaging spectrometer capable of simultaneously recording spatial and spectral data from a rapidly varying target scene. High speed spectral imaging was demonstrated by collecting spectral and spatial snapshots of blackbody targets and combustion products. The instrument is based on computed tomography concepts and operates in a mid-wave infrared band of 3.0 to 5.0 micrometers . Raw images were recorded at a frame rate of 60 fps using a 512 x 512 InSb focal plane array. Reconstructed object cube estimates were sampled at 46x46x21 (x, y,(lambda) ) elements, or 0.1 micrometers spectral sampling. Reconstructions of several objects are presented.

An iterative method of reconstructing degraded images is developed from consideration of a mixed-noise imaging situation. Both photon noise in the image itself and postdetection Gaussian noise are combined by use of the standard maximum-likelihood method to produce a mixed-expectation reconstruction technique that demonstrates good performance in the presence of both noise sources. The new algorithm is evaluated through computer simulations.

A persistent barrier to the wider use of the Computed Tomographic Imaging Spectrometer (CTIS) has been the extraordinary demands it places on computational resources. Raw images can be obtained at snapshot speeds, but reconstructed datacubes typically require minutes of reconstruction time each. We present a new approach to the CTIS reconstruction problem which makes use of the spatial shift-invariance in a CTIS system to greatly reduce the dimensionality of the matrix inversion process performed during reconstruction. Preliminary results indicate that a speedup by a factor of 4000 is possible.

A computed tomography imaging channeled spectropolarimeter (CTICS) is a combination of a computed tomography imaging spectrometer (CTIS) and a channeled spectropolarimeter (CHSP). The CTICS instrument can simultaneously obtain image spatial and spectral information as well as polarization Stokes vectors at each resolution element in a single focal plane array (FPA) integration time with no moving parts. An instrument has been designed and built for the visible wavelength region at the University of Arizona. Performance testing is underway. In this work, we present initial results from data acquired during testing of the CTICS instrument.

Restricted on deposit, 19 Sept 2013, kc / Released with permission of the author, 19 Nov 2013, kc

In hyperspectral imaging systems with a continuous-to-discrete (CD) model, the goal is to solve the matrix equation g = Hθ + n for θ. Here g is a data vector obtained on pixels on a focal plane array (FPA), and n is the additive pixel noise vector. The hyperspectral object cube f(x, y, λ) to be recovered is represented by θ, which is the vectorized set of expansion coefficients of f with respect to a family of functions. The imaging operator is the system matrix H of which its columns represent the projection of each expansion function onto the FPA. Hence an estimate of the object cube f(x, y, λ) is reconstructed from these recovered expansion function projection coefficients. Furthermore H is equivalently a calibration matrix, and amenable to an analytic description. Since the number of expansion functions is large, and the number of pixels on an FPA is large, H becomes huge and very unwieldy to store. We describe a means by which we can reduce the effective size of H by taking advantage of the analytic model of the imaging system and converting H into a series of look-up tables. By this method we have been able to drastically reduce the storage requirements for H from terabytes to sub-megabyte sizes. We provide an example of this technique in isoplanatic and polychromatic calibration of a flash hyperspectral imaging system. These sets of lookup tables are expansion function independent and also independent of object cube sampling.

We present a snapshot technique for performing spectrally-resolved Mueller matrix polarimetry, based on channeled spectropolarimetry. After discussing the measurement theory in detail, we present a simulated measurement of a polymer achromatic retarder. Finally, we review some methods for modifying the technique to achieve improved performance.

We extend recent results for estimating the parameters of a one-dimensional Gaussian profile to two-dimensional profiles, deriving the exact covariance matrix of the estimated parameters. While the exact form is easy to compute, we provide a set of close approximations that allow the covariance to take on a simple analytic form. This not only provides new insight into the behavior of the estimation parameters, but also lays a foundation for clarifying previously published work. We also show how to calculate the parameter variances for the case of truncated sampling, where the profile lies near the edge of the array detector. Finally, we calculate expressions for the bias in the classical formulation of the problem and provide an approach for its removal. This allows us to show how the bias affects the problem of choosing an optimal pixel size for minimizing parameter variances.

We present some new grating designs for use in a computed tomographic imaging spectrometer (CTIS) and discuss their differences with previous gratings. One of the advantages of the new designs is that they provide added flexibility for a tunable CTIS instrument, and we show some preliminary data illustrating this advantage.

A Computed Tomography Imaging Spectrometer (CTIS) is an imaging spectrometer which can acquire a multi-spectral data set in a single snapshot (one focal plane array integration time) with no moving parts. Currently, CTIS instruments use a specially designed computer generated hologram (CGH) to disperse the light from a given spectral band into a grid of diffraction orders. The capabilities of the CTIS instrument can be greatly improved by replacing the static CGH dispersing element with a reconfigurable liquid crystal spatial light modulator. The liquid crystal spatial light modulator is tuned electronically, enabling the CTIS to remain a non-scanning imaging spectrometer with no moving parts. The ability to rapidly reconfigure the dispersing element of the CTIS allows the spectral and spatial resolution to change by varying the number of diffraction orders, diffraction efficiency, etc. In this work, we present the initial results of using a fully addressable, 2-D liquid crystal spatial light modulator as the dispersing element in a CTIS instrument.

Dualband infrared focal plane arrays (FPA) were developed originally for multi-spectral imaging applications, where their advantages in compactness and band-to-band pixel registration, relative to conventional multispectral imagers, were recognized. As dualband FPA architecture is matured for quantum well and mercury cadmium telluride focal plane arrays, and becomes within the grasp of strained layer superlattice technology, applications in addition to multi-waveband imaging come to mind. In various hyperspectral applications that employ gratings, the different grating orders can sometimes be paired with the wavebands of the dual- (or multi-) waveband FPA, allowing high efficiency hyperspectral imaging over very broad wavelength regions. Exploiting the "third dimension" of FPA detecting layers for dual- and multi-waveband capability proved its usefulness for multi-waveband imaging; this paper will show similar advantages for hyperspectral applications and describe such applications.

A spectropolarimeter utilizing an Oriel MIR8000 Fourier Transform Spectrometer in the MWIR is demonstrated. The use of the channeled spectral technique, originally developed by K. Oka, is created with the use of two AR coated Yttrium Vanadate (YVO 4 ) crystal retarders with a 2:1 thickness ratio. A basic mathematical model for the system is presented, showing that the Stokes parameters are directly present in the interferogram. Theoretical results are then compared with real data from the system, an improved model is provided to simulate the effects of absorption within the crystal, and error between reconstructions with phase-corrected and raw interferograms is analyzed. Keywords: Yttrium Vanadate, spectropolarimeter, Fourier transform spectrometer, channeled spectrum. 1. INTRODUCTION The use of a Fourier Transform Spectrometer (FTS) has many advantages over other forms of spectroscopic measurement, such as the use of a diffraction grating, in the MWIR. Predominantly, the FTS maintains the throughput (Jacquinot) and multiplex (Fellgett) advantages.

Abundances of material components in objects are usually computed using techniques such as linear spectral unmixing on individual pixels captured on hyperspectral imaging devices. The effectiveness of these algorithms usually depends on how distinct the spectral signatures in the libraries used in them are. This can be measured by SVD or Least Squares based figures of merit such as the condition number of the matrix consisting of the library signatures. However, it must be noted that each library signature usually is the mean of a number of signatures representing that material, or class of objects. This aspect of how individual library spectral signatures vary in real-world situations needs to be addressed in order to more accurately assess linear unmixing techniques. These same considerations also goes for signature libraries transformed into new ones by wavelet or other transforms. Figures of merit incorporating variations within each library signature (which more accurately reflects real measurements) will be implemented and compared with other figures of merit not taking these variations into account.