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We present simulation and experimental results showing circular polarization is more tolerant of optical collection geometry (field of view and collection area) variations than linear polarization for forward-scattering environments. Circular polarization also persists superiorly in the forward-scattering environment compared to linear polarization by maintaining its degree of polarization better through increasing optical thicknesses. In contrast, both linear and circular polarizations are susceptible to collection geometry variations for isotropic-scattering (Rayleigh regime) environments, and linear polarization maintains a small advantage in polarization persistence. Simulations and measurements are presented for laboratory-based environments of polystyrene microspheres in water. Particle diameters were 0.0824 μm (for isotropic-scattering) and 1.925 μm (for forward-scattering) with an illumination wavelength of 543.5 nm.

Conventional intensity imaging through turbid media suffers from rapid loss of image contrast due to light scattering from particles or random variations of refractive index. This paper features the development of an active imaging, snapshot, system design and postprocessing algorithms that differentiate between radiation that scatters or reflects from remote, obscured objects and the radiation from the scattering media itself through a combination of polarization difference imaging, channel blurring, and Fourier spatial filtering. The produced sensor acquires and processes image data in real time, yielding improved image contrasts by factors of 10 or greater for dense water vapor obscurants.

A white-light snapshot channeled linear imaging (CLI) polarimeter is demonstrated by utilizing polarization gratings (PGs). The CLI polarimeter is capable of measuring the two-dimensional distribution of the linear Stokes polarization parameters by incorporating two identical PGs, in series, along the optical axis. In this configuration, the general optical shearing functionality of a uniaxial crystal-based Savart plate is realized. However, unlike a Savart plate, the diffractive nature of the PGs creates a linear dependence of the shear versus wavelength, thus providing broadband functionality. Consequently, by incorporating the PG-based Savart plate into a Savart plate channeled imaging polarimeter, white-light interference fringes can be generated. This enables polarimetric image data to be acquired at shorter exposure times in daylight conditions, making it more appealing over the quasi-monochromatic channeled imaging polarimeters previously described in the literature. Furthermore, the PG-based device offers significantly more compactness, field of view, optical simplicity, and vibration insensitivity than previously described white-light CLI polarimeters based on Sagnac interferometers. Included in this paper are theoretical descriptions of the linear (S_0, S_1, and S_2) and complete (S_0, S_1, S_2, and S_3) channeled Stokes imaging polarimeters. Additionally, descriptions of our calibration procedures and our experimental proof of concept CLI system are provided. These are followed by laboratory and outdoor polarimetric measurements of S_0, S_1, and S_2.

A compact short-wavelength and middle-wavelength infrared hyperspectral imaging polarimeter (IHIP) is introduced. The sensor includes a pair of sapphire Wollaston prisms and several high-order retarders to form an imaging Fourier transform spectropolarimeter. The Wollaston prisms serve as a birefringent interferometer with reduced sensitivity to vibration versus an unequal path interferometer, such as a Michelson. Polarimetric data are acquired through the use of channeled spectropolarimetry to modulate the spectrum with the Stokes parameter information. The collected interferogram is Fourier filtered and reconstructed to recover the spatially and spectrally varying Stokes vector data across the image. The IHIP operates over a ±5° field of view and implements a dual-scan false signature reduction technique to suppress polarimetric aliasing artifacts. In this paper, the optical layout and operation of the IHIP sensor are presented in addition to the radiometric, spectral, and polarimetric calibration techniques used with the system. Spectral and spectropolarimetric results from the laboratory and outdoor tests with the instrument are also presented.

The theoretical and experimental demonstration of a multispectral Sagnac interferometer (MSI) is presented. The MSI was created by including two multiple-order blazed diffraction gratings in both arms of a standard polarization Sagnac interferometer (PSI). By introducing these high-order diffractive structures, unique spectral passbands can be amplitude modulated onto coincident carrier frequencies. Extraction of the modulated multispectral images, corresponding to each passband, is accomplished within the Fourier domain. This yields a unique multispectral sensor capable of imaging all the passbands in a single snapshot. First, the theoretical operating principles of a PSI are discussed to provide a context for the MSI. This is followed by the theoretical and experimental development of the MSI, which is an extension of a dispersion-compensated PSI. Indoor and outdoor testing and validation of the MSI are performed by observing vegetation, demonstrating the ability of our experimental setup to detect four distinct spectral passbands.

A snapshot imaging polarimeter utilizing Savart plates is integrated into a fundus camera for retinal imaging. Acquired retinal images can be processed to reconstruct Stokes vector images, giving insight into the polarization properties of the retina. Results for images from a normal healthy retina and retinas with pathology are examined and compared.

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.

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.

We present and demonstrate a compact and miniature snapshot imaging polarimeter camera; it is anticipated that such a camera can be scaled down to less than 1.5 cm. Two Savart plates are used at the pupil plane to generate multiple fringes to encode the full Stokes vector in a single image. A geometric ray model is developed to explain the system. The numerical simulation based on this model is presented. Finally, the validity of the device is demonstrated by showing experimental results.

We present several new results on the classic problem of estimating Gaussian profile parameters from a set of noisy data, showing that an exact solution of the maximum likelihood equations exists for additive Gaussian-distributed noise. Using the exact solution makes it possible to obtain analytic formulas for the variances of the estimated parameters. Finally, we show that the classic formulation of the problem is actually biased, but that the bias can be eliminated by a straightforward algorithm.

Thin birefringent prisms placed near an image plane introduce sinusoidal fringes onto a 2D polarized scene making possible a snapshot imaging polarimeter, which encodes polarization information into the modulation of the fringes. This approach was introduced by Oka and Kaneko [Opt. Express 11, 1510 (2003)], who analyzed the instrument through the Mueller calculus. We show that the plane-wave assumption adopted in the Mueller theory can introduce unnecessary error in a polarimeter design. To directly take prism effects such as beam splitting and deviating into accounts we introduce a geometric imaging model, which allows for a versatile simulation of the birefringent prisms and provides a means for optimization. A calcite visible system is investigated as an example, which essentially shows how each design parameter affects the overall image quality and how to modify the polarimeter design to optimize overall performance. The approach is applicable to any prismatic imaging polarimeter with different prism materials and different working wavelengths.

Infrared spectral features have proved useful in the identification of threat objects. Dual-band focal-plane arrays (FPAs) have been developed in which each pixel consists of superimposed midwave and long-wave photodetectors [ Dyer Tidrow , Conference on Infrared Detectors and Focal Plane Arrays (SPIE, Bellingham, Wash., 1999), pp. 434–440]. Combining dual-band FPAs with imaging spectrometers capable of interband hyperspectral resolution greatly improves spatial target discrimination. The computed-tomography imaging spectrometer (CTIS) [ Descour Dereniak , Appl. Opt.34, 4817–4826 (1995)] has proved effective in producing hyperspectral images in a single spectral region. Coupling the CTIS with a dual-band detector can produce two hyperspectral data cubes simultaneously. We describe the design of two-dimensional, surface-relief, computer-generated hologram dispersers that permit image information in these two bands simultaneously.

We report results from a demonstration of a midwave-infrared, nonscanning, high-speed imaging spectrometer capable of simultaneously recording spatial and spectral data from a rapidly varying target scene. We demonstrated high-speed spectral imaging by collecting spectral and spatial snapshots of blackbody targets and combustion products. The instrument is based on computed tomography concepts and operates in a midwave-infrared band of 3.0–5.0 µm. We record raw images at a frame rate of 60 frames/s, using a 512 × 512 InSb focal-plane array. Reconstructed object cube estimates were sampled at 46 × 46 × 21 (x, y, λ) elements, or 0.1-µm 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.

The development of a new error-free digital image compression algorithm is discussed. Without the help of any statistics information of the images being processed, this algorithm achieves average bits-per-word ratios near the entropy of the neighboring pixel differences. Because this algorithm does not involve statistical modeling, generation of a code book, or long integer–floating point arithmetics, it is simpler and, therefore, faster than the studied statistics codes, such as the Huffman code or the arithmetic code.

We have constructed a computed-tomography imaging spectrometer that uses a phase-only computer-generated hologram (CGH) array illuminator as the disperser. This imaging spectrometer collects multiplexed spatial and spectral data simultaneously and can be used for flash spectral imaging. The CGH disperser has been designed to maintain nearly equal spectral diffraction efficiency among a 5 × 5 array of diffraction orders and to minimize diffraction efficiency into higher orders. Reconstruction of the (x, y, λ) image cube from the raw, two-dimensional data is achieved by computed-tomography techniques. The reconstructed image and spectral-signature data compare favorably with measurements by other spectrometric methods.

A temporally and spatially nonscanning imaging spectrometer is described in terms of computed-tomography concepts, specifically the central-slice theorem. A sequence of three transmission sinusoidal-phase gratings rotated in 60° increments achieves dispersion in multiple directions and into multiple orders. The dispersed images of the system’s field stop are interpreted as two-dimensional projections of a three-dimensional (x, y, λ) object cube. Because of the size of the finite focal-plane array, this imaging spectrometer is an example of a limited-view-angle tomographic system. The imaging spectrometer’s point spread function is measured experimentally as a function of wavelength and position in the field of view. Reconstruction of the object cube is then achieved through the maximum-likelihood, expectation-maximization algorithm under the assumption of a Poisson likelihood law. Experimental results indicate that the instrument performs well in the case of broadband and narrow-band emitters.

The index of refraction, n of Phenoxy PKFE, a light yellow plastic produced by Union Carbide, is measured at λ = 588 nm (nD), λ = 656 nm (nC), and λ = 486 nm (nF). These values are of interest because they must be known to determine the optical characteristics of a Phenoxy PKFE lens over the visible spectrum. Lenses made of Phenoxy PKFE have an important advantage over lenses made of other plastics. Phenoxy PKFE is chemically resistant to many epoxy glues commonly used to form airtight bonds in hermetically sealed chambers.

A direct phase measurement interferometer designed and constructed to operate at a 3.8-μm wavelength is described. The interferometer uses a deuterium fluoride laser as the light source, zinc selenide transmitting optics, and a 32- × 64-element PtSi infrared CCD detector array with digital processing electronics and a graphics display on a desktop microcomputer. The instrument, which is useful for measuring a figure error caused by thickness variations in dielectric coatings applied to infrared optics, gives a wave front measurement repeatability of <λ/50 rms.

This paper presents the results of a preliminary evaluation of a platinum silicide (PtSi) Schottky CCD as an imaging array for astronomical applications. The work was done in the near-infrared (1.2 μm < λ < 2.5 μm) spectral regime, where there is presently a lack of commercially available panoramic arrays with acceptable performance. During an initial test run, the array detected a star of magnitude 3.5 using an integration time of 128 msec. Proper optimization of the readout electronics, cryostat configuration, and matching of the telescope image scale to the pixel size could allow detection of a source ~100 times fainter in a 1-sec integration time. This paper will discuss the array architecture, measurement and signal processing techniques, and the observatory and laboratory evaluation tests.

The bidirectional transmittance distribution function (BTDF) is used to evaluate the scattering properties of chemically vapor-deposited (CVD) zinc selenide (ZnSe). Conceptually, the BTDF is a logical extension of the bidirectional reflectance distribution function (BRDF) relation. A working equation for BTDF based on the practical limitations of the instrumentation has been developed. The practical limitations inherent in making BTDF measurements are the finite detector size, the two scattering surfaces of the sample, and the linear radiometric responses of the detector. The instrumentation used to measure BTDF and the data collection procedure are described. Plots of BTDF vs angle from the sample normal are presented for CVD ZnSe at room temperature. The plots are for three thicknesses of ZnSe (6, 19, and 25 mm) at three laser wavelengths (0.6328, 3.39 and 10.6 μm).

Fog spectral transmission data generated in the Electro-Optical Test Facility and propagation models used by the authors are presented. Preliminary results of a modeling effort are presented that support the following conclusions: (1) atmosphere emission is a major factor in IR system performance despite the fact it is commonly omitted; (2) the 3.5–4.1-μm interval offers superior performance to the 3–5 band at both relatively short and long ranges; and (3) the longer wavelength 9.5–11.5-μm band is superior to either the 3–5 or 3.5–4.1 bands in the presence of fog.

This paper discusses the application of a synthetic aperture system (SAS) for the formation of infrared, images. The SAS of primary interest is a hexagoiial array of six circular apertures; special emphasis is placed on a one-dimensional model that describes the salient features of the two-dimensional model. In infrared images, in the 8–14-μm region, conventional detectors are too large to sample the image without aliasing the spatial spectrum. The unusual transfer function characteristics of the SAS are shown to obtain larger sampling distances than those required by the Whittaker-Shannon sampling theory. One possible detector array that will correctly sample the image is presented.

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.