Performance of reflection polarizers using bare semiconductor substrates in the visible and UV spectral range is presented. Performance evaluation based on extinction ratio, throughput, and sensitivity to angular and spectral variations of Si and Ge reflection polarizers are considered.

Pure yttrium vanadate crystals (YVO₄) have optical properties ideal for polarizers in the mid-IR spectrum. YVO₄ is highly transmissive from 400 to 3800 nm and is optically useful to 5 micrometers . YVO₄ is a positive uniaxial crystal with a birefringence larger than the negative uniaxial crystal calcite. The positive birefringence of YVO₄ gives ordinary polarization to the beam transmitted by the polarizer, producing a desirable symmetric field-of- view for all standard designs. Glan, Wollaston, and Rochon polarizers were fabricated from YVO₄ and tested. The preferred Glan design for YVO₄ is Glan-Taylor as for calcite. YVO₄ has advantages in large aperture size, excellent optical quality, high laser-damage threshold, and excellent optical working ability with only a slight tendency to cleave. New monolithic crystal polarizer designs will be described. It is also believed that YVO₄ would be an excellent synthetic substitute for calcite in the visible spectrum.

An optical device for modulation of the intensity of unpolarized light was constructed. In comparison with other modulators, this apparatus allows to reduce the loses of energy of light and preserve its angular divergence. The switching time and contrast ratio of the modulator are 50microsecond(s) and 300, respectively.

Several recent studies have investigated the optimization of Stokes vector polarimeters with respect to signal to noise ratio (SNR). While SNR is an important consideration, performance of a polarimeter in the presence of errors in the calibration and alignment of the optical components is also important. Here, the relationship between system condition and error performance is investigated, and it is shown that an optimum system from the point of view of SNR is not always an optimum system with respect to error performance. A detailed theory of error performance is presented, and the relationship between system condition and systematic errors is described. For systems that over determine the Stokes vector to improve error performance, the RMS error of a SV polarimeter is shown to fall off as the inverse of the number of measurements taken.

An optimization of a dual-rotating-retarder Mueller matrix polarimeter is performed by minimizing the condition number of the system data reduction matrix. The optimum retardance for the rotating retarders is found to be 127 degrees. If exactly 16 intensity measurements are used for the calculation, we observe a complex relationship between the condition number and the size of the angular increments of the two retarders. If many intensity measurements are made, thus over-specifying the calculation, we find broad optimal ranges of angular increments of the two retarders that yield essentially equal performance.

Performance reported efforts to calibrate a MWIR imaging polarimeter met with moderate success. Recent efforts to calibrate a LWIR sensor using a different technique have been much more fruitful. For our sensor, which is based on a rotating retarder, we have improved system calibration substantially be including nonuniformity correction at all measurement positions of the retarder in our polarization data analysis. This technique can account for effects such as spurious optical reflections within a camera system that had been masquerading as false polarization in our previous data analysis methodology. Our techniques will be described and our calibration results will be quantified. Data from field-testing will be presented.

The Air Force Research Laboratory is interested in developing techniques for characterizing and discriminating satellites in Low and Geo-synchronous Earth Orbit (LEO and GEO). Certain materials used in constructing satellites possess unique polarization and wavelength dependent properties that may be useful for satellite discrimination and classification. In this work, we use the TASAT simulation to produce polarization renderings of detailed satellite models, with active and passive illumination, to predict polarization signatures of satellites in various Earth orbit scenarios. TASAT is a detailed tracking and controls simulation developed for modeling electro-optic tracking and imaging scenarios. Polarization renderings from passive illumination provide Stokes parameters representative of material polarization effects for the observed wavelength bands. Active illumination allows the incident polarization state to be changed. Thus, with suitable illuminating states and corresponding Stokes measurements, Mueller matrices may be formed from the active satellite returns, providing additional polarization signature information. Degree-of-polarization (DOP), diattenuation and retardance values calculated from the Stokes parameters and Mueuller matrices provide the polarization signature needed to test for satellite discrimination. We examine the variation of these polarization signatures for different satellite models situated in LEO and GEO observation scenarios. Signature variations for a visible and IR wavelength are considered. The results provide an indication of the feasibility of using material polarization properties for satellite discrimination to within the accuracy of our current materials database and polarization rendering capabilities.

We show that antireflection-coated (ARC) optical systems with numerical apertures < 1 exhibit negligible polarization aberrations of the fourth and sixth order for the retardance and di-attenuation, respectively. Results for ARC high-index optics are presented as examples.

We present and analyze a technique for snapshot imaging spectropolarimetry. The technique involves the combination of channeled spectropolarimetry with computed tomography imaging spectrometry (CTIS). Channeled spectropolarimetry uses modulation to encode the spatial dependence of all four Stokes parameters in a single spectrum. CTIS is a snapshot imaging spectrometry method in which a computer-generated holographic disperser is employed to acquire dispersed images of the target scene, and both spatial and spectral information is reconstructed using the mathematics of computed tomography. The combination of these techniques provides the basis for a snapshot imaging complete Stokes spectropolarimeter which can be implemented with no moving parts. We present results of a simulation that we did using four input Stokes vectors that varied with wavelength. The reconstruction took into account dispersion from the retarders and that low frequency components will be missing in CTIS.

Channeled spectropolarimetry is a technique for measuring the spectral dependence of the polarization state of light. Passive polarization optics are used to encode the spectral dependence of the four Stokes components s_k into a single irradiance spectrum. We treat the technique as a linear operator and compute its singular value decomposition numerically. The resulting singular functions divide into three distinct groups representing s₀, s₁ and mixtures of s₂ and s₃. The corresponding singular values indicate that measurements of the latter two groups will have signal-to-noise ratios reduced form that of s₀ by factors of 0.6 and 0.4 respectively. The structure of the singular vectors is in agreement with a separate estimate of the system's resolution.

Polarization issues drive the design of fiber optic communications systems. The polarization properties, polarization dependent loss (PDL), retardance, polarization mode dispersion, and depolarization of many fiber system components must be controlled to tight specifications. This demand for tight component quality is leading to new generations of improved polarization measurement system for fiber optics. Because of the complexity of polarization properties and their interaction in fiber systems, Mueller matrix measurements are recommended for those components, such as thin films and polarization controllers, which have combinations of polarization mode dispersion and polarization dependent loss.

Efforts to understand the potential for polarization information to improve our target acquisition capability have been extended from the mid and long wave IR regions into the short wave IR. A passive, complete rotating- retarder Stokes imaging polarimeter has been developed, calibrated, and field tested. A review of the calibration and some example phenomenology will be presented, including temporal variation of target polarization signatures. Spectral investigation of targets and backgrounds in the SWIR band have been promising. For daytime use, passive polarization imaging could provide additional information for improved detection or identification. The passive polarization imaging effort in the SWIR forms one half of an active polarization agile 1.54 micrometers imaging system. In this system, the polarization of radiation from an eye-safe 1.54 micrometers laser is controlled so that a target or background can be illuminated with a known polarization. Analysis of the reflected beam allows calculation of the Mueller Matrices will hopefully lead to better target-to-background discrimination. This Active Mueller Imaging Ellipsometer has been calibrated, and initial imagery of targets has been collected.

A near IR Stokes imaging polarimeter is described. Basic principles of operation are presented, system specifications are given, and polarization elements are characterized. System control software and data reduction techniques are briefly explained. Examples of scenes collected as visible photos, visible and near IR intensity images, and visible and near IR polarization images are presented.

The polarizing optics that are being developed for the Solar UV Magnetograph Investigation (SUMI) are described. This polarimeter is being designed for a sounding rocket payload which will make simultaneous measurements of two magnetically sensitive lines CIV and MgII. With a limited observing program, the polarizing optics will be optimized for circular and linear polarization measurements in active regions. The Q polarization will represent exploratory measurements of the transverse field in strong sunspots. This paper will give a brief overview of the SUMI instrument and its scientific goals, will describe the polarimeter that will be used in the sounding rocket program, and will present some of the measurements that have been made on the SUMI polarization optics.

Recent interest in the utility of polarimetry for military and commercial applications has led to the development of many different imaging polarimetric systems. Much of the attention has focused on time-sequential acquisition systems. These systems use a rotating retarder or polarizer with data acquisition times that range anywhere from 10 to 100 seconds. This length of time is needed to capture the required frames of data used to construct a polarimetric image. Consequently, scene changes during data collection will either induce false polarization effects or induce mis- registration effects. These can occur in scenes where the target, background or sky is changing intensity rapidly or in cases where the target or sensor is in motion. To overcome these limitations SY Technology Inc. is developing and testing a 4 camera polarimetric imaging system capable of simultaneously capturing the needed frames to produce a full-stokes polarimetric image. The system operates in the visible to near IR spectrum and is capable of a 25Hz Stokes image frame rate. This paper will summarize the design, components and calibration of a 4 camera polarimetric system.

The polarizing characteristics of materials such as paints, metals and dielectrics, are distinct. Measurements of the Stokes vector or the Mueller matrix provide quantitative information about the material characteristics. This paper describes a laboratory experiment, performed under the support of the US Air Force Research Laboratory, the results of which establish the ability to numerically distinguish materials using a non-imaging active laser system. Such an approach is described in the literature as sub-pixel de- mixing.

This paper describes a novel spectroscopic ellipsometer using no mechanical or active components for polarization modulation. A pair of fairly-thick birefringent retarders are incorporated into the ellipsometer so that the spectrally-resolved ellipsometric angles (Psi) and (Delta) can be determined at once from only the single channeled spectrum. Its effectiveness is demonstrated with SiO₂ films deposited on Si substrates.

The analysis of a new in-line fiber-optic ellipsometer in the polarimetric configuration is presented. The main idea of the system operation is based on controlled birefringence modulation on a piece of standard single-mode fiber followed by an identification of the input polarization parameters change by a suitable detection of different harmonics of the output signal. The paper presents results of system investigation for polarized and partially polarized light. Finally, some experimn4etal results of constructed system action are presented and discussed.

We report on the theoretical analysis, measurement and active rectification of depolarization caused by the differential transmission and phase shift of p- and s- polarized components of an axial beam passing through lens surfaces. Our theoretical analysis finds the polarization of output rays as a function of the input ray parameters, the shape factor and refractive index of the lenses used. For rays that are inclined to the optical axis we find optimal lens shape factors that minimize the rays' polarization aberrations. We report measurements of polarization aberrations that were detected in the back-focal plane of a modern microscope equipped with high numerical aperture lenses. Finally, we discuss strategies for polarization rectification and introduce new designs including a liquid crystal rectifier that can actively compensate a wide variety of polarization aberrations.

The paper covers an autocollimating fiber optic sensor for measuring the birefringence of bulk material based on the use of a pulsed laser and multimode optical fiber with a fiber delay line. The specimen birefringence is defined by measurement of the pulse intensities. The basic expressions that describe the operation of the sensor are presented. The suggested scheme can be used for studying ht inner stress in transparent solid bodies, birefringence of crystals, or for measuring temperature, pressure, electrical and magnetic field strength, etc.

At present there exist some approaches to Mueller-matrix description of depolarization ability of studied object in elastic light scattering. However, as analysis have been carried out in the present paper have been carried out in the present paper have shown all of them are characterized with some essential demerits inherent in approaches pointed out above.

Focal plane wide band IR imagery will be compared with visual wide band focal plane digital imagery of a camouflaged B-52 bomber. Extreme enhancement is possible using digital polarized imagery. The experimental observations will be compared to theoretical calculations and modeling result of both specular and shadowed areas to allow extrapolations to the synthesis of the optical polarization signatures of other aircraft. The relationship of both the specular and the shadowed areas to surface structure, orientation, specularlity, roughness, shadowing and the complex index of refraction will be illustrated. The imagery was obtained in two plane-polarized directions. Many aircraft locations were measured as well as sky background.

The integration and calibration of a hyperspectral imaging polarimeter is described. The system was designed to exploit subtle spectral details in visible and near-IR hyperspectral polarimetric images. All of the system components were commercial-off-the-shelf. This device uses a tunable liquid crystal filter and 16-bit cooled CCD camera. The challenges of calibrating a hyperspectral polarimeter are discussed.

Modeling of polarized radiances in the visible through IR regions requires consistent models for reflectance and emittance of materials. These models must include common effects such as directionality and spectral shape. We have started from a well validated but non-polarized Bi- Directional Reflectance Distribution Function/Directional Emittance model and have added in the polarization state description via Fresnel scaling. The methodology is discussed along with our approach to dealing with possible inconsistencies. Results are demonstrated within a complete 3D polarized object model.

Imaging sensors to detect circular polarization, which have high sensitivity and high frame rates and are light weight and portable, have not been developed. In this paper, we report on our development of novel microscale achromatic retarders. A 2D array of these retarders can be combined with an array of linear polarizers in an imaging sensor. This sensor will be able to capture images of the four Stokes parameters over a wide wavelength band. The achromatic retarder is a combination of two single-order waveplates. Each single-order waveplate is a surface-relief grating. We have calculated the retardance of the combination, using effective medium theory. For light at normal incidence on the achromatic retarder, the retardance is nearly independent of wavelength in the range 3-5 microns and deviates forma mean value of 90 percent by less than 1 percent. We also show that, as field angle is increased, the retardance of our composite retarder deviates less than the retardance of a waveplate formed from a single surface- relief grating. Another advantage of the composite structure is than the achromatic retarder can be fabricated with large aperture on large area substrates.

The color of the ocean and estuarine waters are key indicators of pollutants as well as biological phenomenon. However atmospheric aerosols can be produce a significant bias in the observations. Of particular importance is dust from the Sahara and Gobi Deserts on the Atlantic and Pacific Ocean photometric observations. Polarization can be used to deconvolute the effects of aerosols. In comparison to non- absorbing aerosols, the desert aerosol has opposite behavior for epsilon function with wavelength. Results show the degree of plane polarization decreases with the increase of the aerosol optical thickness and is wavelength dependent. The degree of polarization increases as the viewing zenith angle increase. An additional fallout of this analysis is the effect of aerosols on the ocean heat exchange; warming or cooling can occur depending upon the optical properties of the aerosols. Further, the visibility of military targets is strongly a function of aerosol scattering properties.

The Institute for Space Sciences at the Free University Berlin has built an instrument for hyperspectral measurements (FUBISS). A new polarization entrance optics and a motion control unit is going to be adopted to that system to open up the possibility to derive hyperspectral polarization measurements in the atmosphere in the spectral region from the visible to the near IR. The system is ground based and includes the ground based version of the aureole Sun-Photometer FUBISS-SIRA and FUBISS-ASA. The polarization measurements enable the calculation of the stokes vector and the degree of polarization measurements enable the calculation of the stokes vector and the degree of polarization and angle at predefined incident viewing angles. One possible application will be the characterization of aerosols by retrieving profiles of their optical and micro physical properties.

There is evidence that polarimetric contrast differences in images are band-dependent. Some previous evidence is reviewed. We fabricated and tested a hyperspectral imaging polarimeter that we reported previously. This device uses a tunable liquid crystal filter and a 16-bit camera. The polarimeter is designed to work in the visible and in the near IR spectral region. We present here some examples of imagery collected with this senor, and show how this data may be used to provide superior target discrimination if used selectively, with the appropriate algorithms.

Exploitation of polarization increases the contrast in imaging sensor and makes reconnaissance and surveillance sensors more efficient. This paper reports about two methods of polarization measurements. The used equipments are two IR Thermo vision 900 cameras, one in the wavelength region 3-5 micrometers and the other in the region 8-12 micrometers . The cameras have polarizing filters in front of the sensors. A calibration method is applied. In that way it is possible to correct for the signal contribution from the polarizing filters. The contribution can be separated into two parts, one consists of contributions to the detector signal due to the temperature of the filters and the other consists of reflections at the filter surfaces. The measurement methods are illustrated by laboratory measurements of surfaces of different surface roughness. The objectives of these measurements are to understand the physical properties of different surfaces for camouflage work. Also, calibrated sensitive polarization measurements of backgrounds are reported. The methods make it possible for the sensors to increase their ability for detection, recognition and classification.

This paper will describe a new vector magnetograph that has been developed at Marshall Space Flight Center. This magnetograph was a test ed for space flight concepts. One of those concepts that is currently being tested is the increased sensitivity to linear polarization by replacing electro-optical and rotating waveplates with a rotating linear analyzer. Our paper will describe the motivation for developing this magnetograph, compare this instrument with traditional magnetograph designs.

A brief history of RADAR development is followed by an indication of the relevance of LIDAR to ranging and detection of targets. Initially, radiated laser power is discussed. Peak power of 100 kilowatts with a diode pumped solid-state laser appears feasible. Frequency control appears possible with atomic standards controlling the high power laser. Optical characterization of the polarization properties of lasers on targets is being pursued as well as the options. Coherence length of LASER radiation still poses a problem over ranges beyond one hundred meters. Target identification is enhanced using polarization with the aid of higher-resolution focal plane arrays. Coherence applications appear feasible in the near future.

Fiber-optic inner core gratings are considered together with the non-uniform Deformations is oscillated optical fiber. This is wide method of vibration registration as a result of appropriate deformations. Analysis was done for fiber cantilevers with the length 1-10 mm. Different cases were analyzed that correspond to transverse and longitudinal vibrations of the fiber tips or fragments with tow clamps. The pi-shifted Bragg-gratings are discussed to measure of vibrating amplitude in different real cases.

In this paper we outline and address some of the challenges encountered in calibrating a visible 4-channel imaging reduced Stokes polarimeter. Specifically we expose the errors associated with the retardance of the optical elements in the system and show how the presence of circular polarization can affect the measurement of the linear states of polarization. These errors are analyzed in some detail and several possible solutions are proposed.

Relatively little work has been performed to investigate the potential of polarization techniques to provide contrast enhancement in natural scenes. Historically, this has been because film is less accurate radiometrically than digital CCD FPA sensing devices. Such enhancement is additional to that provided by between-band differences for multiband data. In them id 1990s, Kodak developed several digital imaging cameras, which were intended for professional photographers. The variant we used produced images in the green red and near IR, simulating CIR film. However, the application of linear drivers to read the data from the camera into the computer resulted in a device, which can be used as a portable multiband imaging polarimeter. Here we present examples to examine the potential of digital image acquisition as potential quantitative method to obtain new information on natural landscapes additional to that obtained by multiband or even hyperspectral imaging methods.

Including polarization signatures of material samples in passive sensing may enhance target detection capabilities. To obtain more information on this potential improvement, a simulation is being developed to aid in interpreting IR polarization measurements in a complex environment. The simulation accounts for the background, or incident illumination, and the scattering and emission from the target into the sensor. MODTRAN, in combination with a dipole approximation to singly scattered radiance, is used to polarimetrically model the background, or sky conditions. The scattering and emission from rough surfaces are calculated using an energy conserving polarimetric Torrance and Sparrow BRDF model. The simulation can be used to examine the surface properties of materials in a laboratory environment, to investigate IR polarization signatures in the field, or a complex environment, and to predict trends in LWIR polarization data. In this paper we discuss the simulation architecture, the process for determining and roughness as a function of wavelength, which involves making polarization measurements of flat glass plates at various angles and temperatures in the laboratory at Kirtland AF Base, and the comparison of the simulation with field dat taken at Elgin Air Force Base. The later process entails using the extrapolated index of refraction and surface roughness, and a polarimetric incident sky dome generated by MODTRAN. We also present some parametric studies in which the sky condition, the sky temperature and the sensor declination angle were all varied.