This paper provides a characterization of the fields of light polarization with which the optical designer or user of optical devices in the natural environment must be concerned. After a brief historical outline of the principal developments in polarization theory and observations during the last two centuries, the main emphasis is on the two primary processes responsible for the polarization of light in nature--scattering of light by particles of the atmosphere and reflection from soils, vegetation, snow, and water at the earth's surface. Finally, a seven minute film on polarization effects which can be seen in everyday surroundings will be shown. Scattering by atmospheric particles is responsible for high values of polarization in various atmospheric conditions and at certain scattering geometries. Such scattering particles include molecules of the atmospheric gases, aerosols of dust, haze, and air pollution, water droplets of fog and clouds, and the ice crystals of cirrus. It is seen that development of the theory of scattering by such particles has outstripped the measurements necessary for validation of the theory, a fact which points up the importance of symposia such as the present one. The reverse is true, however, for the polarizing properties of natural surfaces. Only in the case of still water is the theory of reflection adequate to characterize in a quantitative fashion the polarizing effects produced by the reflection of light from such natural surfaces. Polarization of light by reflection from vegetation is of prime importance in a remote sensing context, but much further work is needed to characterize vegetative reflectance for the purpose. The short film on polarization effects provides a good visualization technique and training aid for students interested in the field.

Relatively little attention has been paid to the potential of polarization techniques to provide additional information for the mapping of earth resources, compared to the published work concerning other active and passive remote sensing systems. Recently, a substantial number of polarized light images of a variety of terrestrial scenes have been obtained from the Space Shuttle. A boresighted pair of Hasselblad cameras was used, in which polarization filters were fitted. The polarization directions were perpendicular to each other for the two cameras. Image pairs were acquired with one image being of maximum intensity, and the other showing minimum intensity. Selected pairs of images, obtained using black and white films, were digitized. The images were registered and compared, using digital image analysis techniques. Differences due to polarization were observed, these included intensity and contrast differences, together with differences in the spatial frequency, orientation and population of observable contrast boundaries. It was found empirically that some digital image analysis techniques enhanced the differences. A comparison of the enhanced difference images, obtained from the polarization pairs, with the intensity data that would have been obtained without the aid of polarization filters, confirms that a considerable degree of new, useful information may be obtained by the use of polarization techniques. This new information was most helpful in better defining the observed ground features in the cases studied. This is because the better definition of contrast boundaries, improvement of contrast across boundaries, improvement of shadow detail and reduction of noise level increases the useful information in an image, and improves its interpretability.

Polarization in terrestrial remote sensing has reached the operational phase with the implementation of an experiment aboard the Space Shuttle. The system requirements for a polarimetric analyzing system are discussed and the rationale for polarization measurements is developed. Polarization is a sensitive indicator of cloud particle size distribution, soil texture. atmospheric aerosols/haze. and sea state. Focal plane arrays are ideally suited for focal plane measurements.

NASA's In-Situ Contamination Effects Facility, Marshall Space Flight Center will be used to measure the polarization scattering from optical surfaces due to outgassed molecular contamination. Measurements will be taken using a non-coherent vacuum ultraviolet (VUV) source at 123.6 nm and a set of three solar blind VUV photomultipliers. An in-plane VUV BRDF experiment is described and details of the on-going program to characterize optical materials exposed to the space environment is reported.

To date polarization observation have been acquired from five Shuttle missions. These observations, consisting of some four hundred pairs of polarized images of Earth, demonstrate both the potential of applying polarization as an added dimension in remote sensing, and the complexity involved in doing so. Following the acquisition and preliminary analysis of the data, a workshop on Remote Sensing in Polarized Light was convened at the NASA, Johnson Space Center to consider follow-on options. A three-phase program was recommended by the workshop members with all phases using the Space Shuttle as the observation platform. The Shuttle has some constraints in supporting observations of the type required to obtain a better understanding of the complexities in applying polarization in remote sensing. However, it has many attributes, foremost being the human presence which provides the real time feedback required to get the most information out of any given scene. A description of these constraints and attributes will be provided along with the recommendations resulting from the workshop and descriptions of the past and future observing procedures used from Shuttle.

Techniques using polarized infrared energy have a potential for developing passive sensors that detect man-made objects in complex natural backgrounds. This detection has the potential of improving the performance of various military systems. This paper addresses the physics of the polarization process, describes the characteristics of targets and backgrounds, and shows how one can compute the polarization seen by a detector. Most natural backgrounds appear to be unpolarized. However, the performance of polarized detection techniques will depend on the degree of polarization clutter encountered; a measurement program is needed to determine the extent of this background polarization clutter.

Modeling the properties of polarization modeling is of importance in both geometrical and physical optics modeling. Most of the geometrical theory is directly applicable to the physical optics calculations but there are special considerations in implementing polarization in diffraction codes and such effects as spatial filters and near-field diffraction can be treated which are difficult or impossible with geometrical calculations. The discussion of modeling is general but application to waveguide grating couplers for optical data storage is treated as an interesting special case. This paper discusses a program to add polarization properties to a physical optics code. Physical optics codes have been developed over the last 20 years to analyze lasers resonators and beam trains. The polarization features have been added to a general purpose diffraction code called GLAD [1]. The specific program supported by this research is optical data storage with a special application to waveguide grating couplers. Our objective is to treat all types of systems with polarization and diffraction aspects -- conventional and those with integrated optics components. The first decision to be made is whether to treat polarization with Jones or Mueller matrices. Physical optics calculations generally deal with strictly coherent light so a case may be made for using the simpler Jones matrices. A second argument is that it is best to proceed with the simpler Jones methods before attempting to implement the more complex 4-vector treatment. In beam propagation studies, we commonly use complex arrays ranging in size from 32 X 32 to 1024 X 1024 with the most common sizes being between 64 X 64 to 256 X 256. These matrices are propagated with standard Fourier optics propagators [2]. The information required for a physical analysis is clearly much greater than for a geometric optics ray trace, which may require only a few rays to at most several hundred. One must take somewhat more care to develop efficient procedures so that the tens of thousands to hundreds of thousands points can be treated efficiently. However, in our studies the diffraction propagation remains the most time consuming task. In Jones calculus treatment, it is only necessary to have two complex numbers per point, for example Es and Ep where s and p are orthogonal polarization states. We simply use two complex amplitude arrays. The wavelength is of course identical for both arrays and for isotropic materials the index is also the same. For slightly anisotropic materials, it still may be possible to treat propagation of both arrays identically with the addition of a phase lead or lag. Thus the propagation time is doubled. Not only do the two arrays share the same wavelength and (almost) the same index of refraction, the spatial subtense of the two arrays is (almost) the same. We can treat the case of anisotropic materials and propagation at arbitrary angle with respect to the OPTICAL axis, which can introduces shear of the two polarization states, an an incremental effect. Since the arrays subtend the same physical space, we can treat the polarization properties by putting the polarization operations inside the inner most loop as shown in Table 1. Commonly we have more than one optical beam and the outer loop is generally a scan over all optical beams present

Reading of magnetooptically recorded data relies on the detection of light whose polarization state varies very slightly with the direction of magnetization of the sensitive layer of the disk. Because the change in polarization is so small, differential detection methods are used, and a number of features of the optical detection scheme can adversely affect the polarization and the signal levels. Among those features considered are the polarization of the laser itself, optical surfaces within the head, substrate birefringence, and optical feedback.

Methods are presented for the interpretation of the polarization aberration of optical systems. The polarization properties of ray paths through optical systems are classified as diattenuating and/or retarding and as circular, linear, or elliptical via the eigenvalues and eigenpolarization states of the associated Jones matrix. Polarization elements are classified as homogeneous if the eigenpolarization states are orthogonal, and inhomogeneous if they are not. It is shown that the maximum coupling of light from the incident to the orthogonal polarization state occurs when the incident light is in a polarization state which is an equal mixture of the eigenpolarizations of a homogeneous polarization element. Two examples of polarization aberration functions are given, for the radially symmetric system, and for the circularly retarding lens. Simple algorithms are provided to determine aberration coefficients from the polarization ray trace of a few rays. The examples demonstrate how polarization aberration introduces wavefront aberrations and apodization which vary with changes in the incident polarization state.

The objective of a number of optical instruments is to measure the intensity accurately without bias to incident polarization state. One method to overcome polarization bias in optical systems is the insertion of a spatial pseudodepolarizer. Both the degree of pseudodepolarization and image degradation (from the polarization aberrations of the pseudodepolarizer) are analyzed for two depolarizer designs: the Cornu pseudodepolarizer effective for linearly polarized light and the dual Babinet compensator pseudodepolarizer effective for all incident polarization states. The image analysis uses the matrix formalism presented in a previous paper ("Diffraction image formation and analysis in optical systems with polarization aberrations I: Formulation and example") to describe the polarization dependence of the the diffraction patterns and optical transfer function.

Radiative transfer in an atmosphere-ocean system has, until recently, concentrated on radiance calculations involving the scalar theory. The only correct approach is to include the full Stokes vector treatment. The authors have developed a very powerful Monte Carlo program which utilizes the method of correlated samples to calculate simultaneously both the scalar and vector radiances using the same photon histories. This technique has an advantage. Though the absolute radiances may be in error by a significant amount, the relative differences can be quite accurate. Complete inhomogeneity in both the atmosphere and ocean can be handled as long as the Mueller matrix for the scattering processes is known. The program is also able to accurately incorporate a stochastic dielectric interface. The error analysis will be presented as a function of both the inherent optical properties of the ocean and a calm wind.

In the present paper we discuss the imaging qualities of a birefringent lens. The transmittance of such a lens, sandwiched between two polarizers, varies radially. The fact that the nature of this radial variation of transmittance can be controlled by changing the orientations of the two polarizers relative to the optic axis of the birefringent lens, may be utilised for continuously modifying the imaging characteristics of the lens. The study of the point spread functions (PSF) of such a polarizer-birefringent lens-polarizer combination reveals that this can be utilised both for achieving apodisation and superresolntion.

The order dependence of weak polarization elements is investigated and it is shown that weak polarization elements are very weakly order dependent; if the diattenuation or retardance is a small term, the order dependence is a higher order term. This has particular application to the polarization properties of an arbitrary ray path through a sequence of antireflection coatings. The polarization properties are explored through expansion of Jones matrices into sums of Pauli spin matrices. It is shown that the polarization properties of a meridional ray path are independent of the order in which the interfaces are encountered, and that the ray path will act as a linear diattenuator aligned or perpendicular to the meridional plane and/or as a linear retarder aligned or perpendicular to the meridional plane. A skew ray does have order dependence in its polarization properties. Due to these order dependent terms, the ray path in general acts as an elliptical diattenuator and/or retarder, despite the fact that all individual interfaces act only as linear polarization elements.

The impetus for this paper was to assist investigators not familiar with radiometry theory. Many times they apply a scalar theory to scattering of polarized light from non-depolarizing targets. Also some investigators erroneously apply a combined scalar-vector theory since the correct vector-matrix approach has not been developed in the literature. The classical theory used by many investigators was given by Nicodemus, et al. and this theory will be modified in this paper. When incident polarized radiation is incident upon a target it is represented by a Stoke's vector and the interaction with the non-depolarizing surface is given by the (4x4) reflectance Mueller matrix, the scattered light is polarized and is a Stoke's vector. The vector-matrix theory is applied to the various geometries given by Nicodemus and the various types of reflectance matrices are defined in terms of the bidirectional reflectance matrix and the BRDF matrix. These results are presented in a tabular form.

A formalism for treating the effects of arbitrary, but relatively small linear perturbations on the polarization (and related properties) of the two component fundamental guided mode of a single mode optical fiber is presented. The approach is phenomenological in the sense that derived expressions relate to measurable quantities. Hence, the coherency equation of motion (CEM) is derived, integrated, and solved for the general case of arbitrary perturbations. The CEM is transformed to the stokes representation and the corresponding stokes form of the coherency evolution (SCE) or Mueller matrix is solved in closed functional form for several interesting special cases. The formalism was applied to the characterization of Polarization-maintaining fibers (PMF) and the design of PMF birefringent wavelength filters. The formalism has proven to be a powerful tool in calculation and design. In addition, the theory is in excellent agreement with measured data.

A polarization analysis capability based upon polarization raytracing is described. The polarization ray trace can model the effects of various interface types including metallic reflectors and multilayer coatings. Idealized retarders and linear polarizers can also be incorporated into the model of an optical system. Information obtained during the polarization ray trace is used to compute image quality metrics such as the point-spread function and the modulation transfer function. In addition, the polarization state of the electric field at any point along a ray path can be found. The utility of the polarization raytracing approach is demonstrated by using the CODE VTM optical design program, which incorporates the modeling features described here, to perform an analysis of selected optical systems, including a corner-cube reflector, a folded beam expander, an imaging radiometer and a high numerical aperture objective.

In this paper we derive the constraints imposed on an arbitrary 4x4 real matrix such that it correspond to a physically realisable Mueller matrix M. These constraints are important, in practice, when M is derived from experimental measurements. Under such circumstances the measured matrix may be filtered to yield two components, one of which is physically realisable plus a nonphysical remainder term. By comparing the relative magnitudes of these two, we obtain a quantitative measure of system fidelity. In the course of this development, we outline two new matrix descriptors of polarised scattering, the system covariance and coherency matrices. These 4x4 Hermitian operators are linearly related to X but yield better physical insight into the scattering phenomena causing depolarisation. We illustrate by reference to rough surface scattering under physical optics.

The precise measurement of micro-images in the fields of surface topography, integrated circuit inspection and microscopy, requires optical sensors and attenuators with wide dynamic range. Polarization techniques with these qualities have long been used in the fields of ellipsometry and polarimetry. This paper describes the use of polarization in a two-channel null microphotometer to quantify various aspects of surface texture such as flaws, waviness and roughness. Recently obtained resultS on the measurement of micro-height variations, texture, line widths and edge location will be presented to illustrate the wide range of metrology possible with this technique.

Utilizing laser's properties of both polarization and temporal coherence , a real time method of moire interferometry is proposed to obtain the separated 3-1) displacement derivative fringe patterns . For dual beams that contain identical polarization components , the optical-path difference is larger than the coherent length to eliminate the interaction between the wavefronts due to the shearing . For dual beams that include no identical components of polarization , the vibration planes are perpendicular to each other to fulfil the frame-separation of the in-plane derivative patterns. The out-of-plane displacement derivative patterns are achieved by the shearing of the zero-order diffractions of the grating.

The Four Detector Polarimeter (F DP) has been described previously by Azzam 1-3. The purpose of this instrument is to provide a fast and accurate means for simultaneously measuring all four Stokes parameters of an arbitrary input polarization state of light. We have designed, built and tested an instrument based on these principles. The instrument is computer controlled and incor-porates special algorithms for calibration and determination of the instrument matrix. This paper will present results obtained for measuring the complete Stokes parameters for light at wavelengths of 633 and 830 nm. We will discuss the calibration considerations in detail and present results for the accuracy of determination of polarization angle, a, and ellipticity, P. In addition we will present results for polarization components such as quarter wave plates, half wave plates and polarizing beam splitters measured using the 1P.

The light scattering properties of leaves are used as input data for models which mathematically describe the transport of photons within plant canopies. Polarization measurements may aid in the investigation of these properties. This paper describes an instrument for rapidly determining the bidirectional light scattering properties of leaves illuminated by linearly polarized light. Results for one species, magnolia, show large differences in the bidirectional light scattering properties depending whether or not the electric vector E is parallel to the foliage surface.

An improved two-channel polarization modulation ellipsometer has recently been developed which has the capability of simultaneously measuring all three components of the reduced Stokes vector of light reflected from a sample surface. In contrast to the more conventional rotating analyzer ellipsometer, this instrument is very sensitive to A when A is close to 0° or 180°, and can measure the quadrant of iv and A. In order to maximize the accuracy and sensitivity of this instrument, new techniques have been developed to calibrate the photoelastic modulator. This paper presents techniques for determining (1) the drive voltage which determines the amplitude of the modulation as a function of wavelength, (2) the modulator static strain as a function of wavelength, and (3) the azimuthal angular orientation of the photoelastic modulator with respect to other optical elements in the system and to the sample itself. Once these calibrations have been performed, very accurate measurements of the ellipsometry parameters can be obtained.

For null ellipsometry, error equations for polarizer and analyzer angles are formulated in terms of the anisotropic defect parameters of the compensator. Errors of δ ψ and δ Δ for dielectric samples are about the same as those for the straight-through case. Explicit analytical solutions of 8v and So for metallic samples are derived in terms of the anisotropic retardations with large deviations from quarter-wave. The analytical solutions agree with the results obtained from the direct computer simulation of the null ellipsometer as well as with the numerical solutions for the error equations.

This paper describes the infrared spectropolarimeter currently under development at the University of Alabama in Huntsville. The instrument, the data acquisition and processing algorithms, and several calibration issues are examined. Results are presented showing measurements of the retardance spectra of polarization elements, and the s- and p-transmission and diattenuation spectra of infrared coatings.

We describe a system for measuring magneto-optical spectra in the 1.5-6-eV photon energy range using a rotating analyzer technique. The measurements are done at a near normal incident angle of less than 2 degrees. A stepping motor with 400 steps per revolution is used to control the analyzer azimuthal angle. After Fourier transformation, the magneto-optical parameter of polar Kerr rotation angle, e is obtained. Magnetic field and spectral scanning, as well as data processing: are totally controlled by a microcomputer. The mechanical and electrical design, alignment, calibration, and error reduction techniques for this sytem are discussed in detail. Application of this system is illustrated for compositionally modulated amorphous (Dy/Co) multi-layer films.

Most ellipsometers are based on the use of high-grade polarizers and accurately-calibrated retarders. An ellipsometer capable of making measurements using less-than-perfect polarizers and uncalibrated retarders has been developed. The instrument uses a single-polarizing element which can be a simple sheet polarizer for the visible range or a wire-grid polarizer for the infrared range. Accurate values of psi and delta can be obtained with an imperfect polarizing element if it is properly characterized at the working wavelength. The instrument uses an incandescent source and a filter or grating monochromator. It is well suited for measurements of the wavelength dependence of psi and delta of multilayer-coated reflectors. The working elements of the ellipsometer are rotated through fixed-angle settings and signal amplitudes are measured. The paper describes the instrument and gives calculations for both perfect and imperfect polarizing elements.

Polarimetry, or transmission ellipsometry, is an important experimental technique for the determination of polarization properties of bulk materials. In this technique, source radiation of known polarization is passed through bulk samples to determine, for example, natural or induced birefringence and dichroism. The laser is a particularly appropriate source for this technique because of its monochromaticity, collimation, and radiant intensity. Lasers of many different wavelengths in different spectral regions are now available. Laser polarimetry can be done in any of these wavelength regions where polarizing elements are available. In this paper, polari-metry is reviewed with respect to applications, sources used, and polarization state generator and analyzer configurations. Scattering ellipsometry is also discussed insofar as the forward scattering measurement is related to polarimetry. We then describe an infrared laser polarimeter which we have designed and constructed. This instrument can operate over large wavelength regions with only a change in source. Polarization elements of the polarimeter are in a dual rotating retarder configuration. Computer controlled rotary stages and computer moni-tored detectors automate the data collection. The Mueller formulation is used to process the polarization infor-mation. Issues and recent progress with this instrument are discussed.

We present our first step toward digital imaging ellipsometry. The microscope objective and an object is located between a polarizer and an analyzer. We rotate the pair of polarizer and analyzer synchronously keeping the angle between them at right angles. At each rotation angle, the microscope image is sampled and stored successively in a frame memory of an image processor. Simple processing on these images provided us a 2-D distribution of retardations and a 2-D map of the directions of principal axes. Polarization-independent brightness variations were successfully removed by preprocessing.

Dielectric multilayer thin film stacks deposited on glass plates or prisms can work as polarizing beam splitters when used at an oblique angle of light incidence. Coatings deposited in vacuum by conventional electron beam or reactive thermal evaporation have an inherently large internal surface area, because of the columnar micro-structure, and have packing densities less than unity. Exposed to ambient humid air, their spectral response and polarization characteristics change. The cause is adsorption or desorption of water vapor on their inner surfaces, upon changes in humidity and temperature. The novel deposition technique of low voltage reactive ion plating produces thin films with a packing density of unity or higher. This prevents. them from any uptake of humidity at all. We demonstrate the fabrication of stable polarizing beamsplitters for the HeNe wavelength of 632.8 nm by this technique. We reported our preliminary results in an earlier presentation.' Here we present also the performance of our samples after their exposure to ambient environment for three months.

There is growing interest in using larger primary mirrors (3- to 4-meter diameter range) as the output optic in various laser systems. A major advantage of this approach is a reduction in the thermal blooming problem when laser beams are transmitted through the atmosphere. Another significant advantage is the increase in focussed intensity, which becomes available if non-uniformities of coatings can be kept to a certain limit. The thickness non-uniformities are caused by the vacuum coating chamber's physical constraints and the coating process. These non-uniformities manifest themselves in three ways, i.e., 1) as variation in spectral reflectivity performance over the clear aperture; 2) as variation in polarization state properties of the coating over the clear aperture; and 3) as figure distortions. This paper deals with the physical constraints of the coating chamber that controls the non-uniformities in thickness and how these thickness non-uniformities affect the polarization and optical figure properties of a coating design. A simplistic coating design is initially selected for a set of two wavelengths and its optical performance over the clear aperture of a 3.6-meter optic is given along with the effect on the optical figure. It was found that this initial design produces phase distortion of opposite signs at the two wavelengths. This causes a problem in that, if the misfigure is partially corrected by focussing for one wavelength, this will aggravate the misfigure for the other wavelength. It has been shown in this paper that a modified, still simplistic design (full- or half-quarter wave design) can be used to correct this problem without appreciably affecting the reflectivities at the wavelengths of interest.

The design of dual wavelength polarizers presents a challenge if a cube configuration is not practical. If the two wavelengths are sufficiently far apart, the design can consist of a quarterwave stack reflector centered between the two wavelengths. This necessitates the proper selection of refractive indices. Further design flexibility can be obtained by introducing spacer layers which result in a Fabry-Perot type of performance. Design techniques are discussed and applied to the following spectral requirements:

Designs of non-polarizing beamsplitters with ratios of R:T = 50:50 and 30:70 over the spectral range of 500 - 600 nm have been verified experimentally with dummy coatings on sheet glass substrates for normal incidence. The making of actual beamsplitters requiring high index incident media (prisms) was hindered by the unavailability of proper prisms at the time this study was presented. The completed investigation and results will be published later in Optical Engineering.

In this paper we describe the results of a polarization-based Strehl ratio analysis for a high energy laser system which includes a large diameter Cassegrain beam expander and a four fold mirror coude telescope. The analysis takes into account coating characteristics and telescope pointing direction changes. Multilayer dielectric coatings on curved optical surfaces in a high-energy laser system will affect far-field system performance due to variations in phase retardance and reflectance across the aperture. Since control of the coating process becomes more difficult as the size of the coated optic increases, systemic coating thickness variations will introduce additional aberrations.

Thin films deposited in high vacuum by thermal evaporation, electron beam evaporation, and ion assisted deposition are anything but smooth, homogeneous, stratified media with plane parallel boundaries as assumed in thin film design and theory. In particular, the porosity brought about by the columnar microstructure of these films has been a problem ever since their first use. The refractive index may change upon exposure to ambient atmosphere, as a result of H2O adsorption. In-situ rapid scanning spectrophotometers and ellipsometers have helped various researchers to determine the degree of index change and the packing density of the films. Low voltage reactive ion plating is a rather novel deposition technique which produces thin films with packing densities of unity and higher. The dense, vitreous or polycrystalline microstructure, which pre-vents the films from adsorbing water upon exposure to air, yields films with bulk-like optical properties that are constant in time. However, there are problems with increased absorption particularly with ion plated TiO2 and SiO2 multilayer thin-film stacks. Continuous measurements of n and k during deposition need to be studied in order to determine the location of the increased absorption. Engineering aspects of mounting a Rudolph Research ellipsometer on a Balzers BAP 800 vacuum system will also be discussed.

Magnetooptical storage systems are designed to obtain high signal-to-noise ratios (SNRs), so that reliable read-back signals are obtained. One characteristic of the optical components in such systems is that they typically introduce a phase shift between the two components of the polarized read-back light. This phase shift reduces the signal amplitude and can increase noise, resulting in reduced SNR. To compensate for the phase shift, and thus restore SNR to the maximum possible value, compensation optics are inserted into the read-back system. This paper discusses various techniques for phase compensation and the characteristics of each technique with respect to alignment and component quality. A Jones calculus model is used to calculate signal and sensitivity to noise currents.

A new instrument for measuring magnetic fields in the sun's atmosphere has recently been installed at the National Solar Observatory in New Mexico. At each point within the field of view, it detects both linear and circular polarization in a spectral line from which the solar magnetic field strength and direction may be deduced. The vector magnetograph has low instrumental polarization and low circular-to-linear crosstalk. Spectral resolution is provided by a solid lithium-niobate Fabry-Perot filter which may be electrically tuned to scan any solar spectral line. The instrument is capable of 0.7 arc second spatial resolution and 0.015 nm spectral resolution. Prior to installation, tests were conducted at the Applied Physics Laboratory to evaluate the polarimeter components. The instrument and its background are described, together with some test results.

One of the operational modes of the European Very Large Telescope (VLT) will be the one in which the four 8.2 meter diameter telescopes will be used together with two or more smaller telescopes with about 2 meter aperture as a spatial amplitude interferometer. One of the main factors affecting the performance of this interferometric array relates to the polarization characteristics of the optics composing the legs of the array. Retardation effects and reorientation of the polarization coordinate frame of reference by reflections are a major cause of fringe contrast decrease (and even disappearance). I have analyzed these effects and developed a raytracing algorithm to calculate the polarization transfer and the resulting fringe contrast decrease.

The performance of a large aperture, high energy laser system with a return wavefront sensor is dependant upon the correct measurement of the beacon wavefront and the resultant phase conjugation of the high energy laser (HEL) beam. However, high reflectance MLD coatings required for HEL systems can introduce polarization changes to the laser beams and wavefront phase errors since the wavefront phase errors can be wavelength dependent. Polarization selective sensors, such as interferometric wavefront sensors, may encounter large variations in intensity across the aperture due to the variation of the polarization state across the aperture. A significant uncorrected wavefront error may result when the beacon and HEL wavefronts differ due to the coatings and the incident polarization state of the beam. Estimation of the wavefront errors introduced into the beacon and HEL beams by the standard coatings is presented. An approach to reduce the intensity variations and wavefront differences is suggested and examined.

Diffraction grating spectrometers exhibit a complex dependance on the polarization state of incident light. We have characterized the polarization properties of a high resolution echelle grating spectrometer. Large variations of instrument response with incident polarization state at ultraviolet wavelengths were found. The Imaging Stratospheric Ultraviolet Spectrometer (ISUS) is a high resolution spectrometer for remote sensing of atmospheric trace constituents. Weak line emissions are observed against the bright, partially polarized Rayleigh scattered sky background. To determine the air density from the Rayleigh scattering intensity the effects of polarization on the spectrometer response must be known. It was anticipated that such polarization effects could be significant in the ISUS instrument, which includes a fold mirror, a cross dispersing plane diffraction grating and an echelle grating. Measurements of the sensitivity of ISUS to linearly polarized light at 312.6 nm showed a peak-to-peak variation of 72% as the plane of polarization is rotated. The results of these measurements are presented and nine elements of the sixteen element system Mueller matrix which describes the behavior of ISUS in partially linearly polarized light are measured. The implications of the observed instrumental polarization for remote sensing observations and its impact on a technique for discriminating against the polarized Rayleigh scattered background to improve the measurement sensitivity are discussed. Subject terms: polarization; spectrometers, polarimetry, polarization aberration; instrumental polarization, Mueller calculus.

Many recording films have polarization properties that can influence and degrade the performance of a coherent optical system. Contrast reduction, amplitude distortion, and wavefront modulation are possible adverse consequences when using these films for data recording, storage, or playback. The polarization characteristics, or a lack thereof, of several film types, three optical adhesives, and five index-of-refraction matching liquids were measured. Unexposed strips of film were developed in D-19 and/or D-76 developer. The developed film strips were immersed in a nonpolarizing index-matching liquid and placed between an incident, linearly polarized laser beam and a crossed analyzer. The film strip was rotated through a full 360 deg., while the light transmitted through the crossed analyzer was measured and the experimental results recorded. These polarization measurements reflect the integrated effect over a circular region of 20-mm diameter. By separating the emulsion from the film backing, the major contribution of the backing to the polarization response was determined. We have modeled the response of a film strip as either an ideal linear polarizer or a birefringent material. A comparison of calculated angular scan with experimental results enables one to characterize the nature of the polarization properties of a selection of samples. A second factor to be considered concerns the "fog" level density of the unexposed film. A high density level or a corresponding low transmission level decreases the power efficiency of the optical system and modifies the contrast ratio. We have found that the fog density varies over a wide range of values for the set of films tested. The transmission data for the developed (i.e., unexposed) films also are reported.

This paper contains a database of references on polarization related topics. The database will facilitate the search for papers dealing with a specific topic, author, etc., and aid in compiling lists of references.

Longitudinal KD* Ps are used in ground-based solar magnetographs to eliminate seeing effects by rapidly changing their retardation characteristics. Although one of the main applications for longitudinal KD*Ps has been their use as a variable retarder for "imaging" applications, an understanding of their limitations is important when developing scientific instruments that make very accurate polarization measurements. This paper will discuss some of the problems associated with the use of these devices in the Marshall Space Flight Center (MSFC) vector magnetograph. These problems include temperature, field of view errors, and electrical characteristics.

Corning has extended the performance of its PolarcorTm near infrared glass polarizers to contrast ratios k1 /k2 of over 10,000. These polarizers offer broader bandwidth, higher transmittance, higher temperature resistance, better durability, and improved contrast (extinction) when compared to plastic and wire grid polarizers. Acceptance angle, cost, and compactness are significantly better than crystal polarizers. Applications include optical isolators, Faraday rotators, magneto-optic devices, fiber optic sensors, Kerr effect devices and optical data storage devices. Polarcor contains elongated, submicron silver metal particles aligned along a common axis. These particles preferentially absorb the polarization component of light which is aligned with the elongation axis of the particles. The mechanism is believed to be resonant absorption by the silver conduction electrons. Careful process control allows the polarizer performance to be optimized at various laser lines, although a wide bandwidth provides polarization over a range of wavelengths. The polarization results from a very thin layer on the surface of the polarizer, thus allowing high contrast from a very thin package. Recent advances in processing have resulted in increases in the contrast ratio from 500 to over 10,000 while maintaining k1 values of 87-91%, depending on wavelength. The corresponding values of Ho and Hgo are 38-41% and 7.6-8.5x10^-5, respectively. Performance may be improved by application of high efficiency anti-reflective coatings. This paper reports on a characterization study of the performance of newly developed Polarcor high contrast polarizers optimized for applications from 725-1550 nm.

The magneto-optic (Faraday) effect in dia-magnetic materials is a promising method of measuring magnetic fields or electric currents in space plasmas due to its non-invasive character. Fiber-optic sensors with coherent detection schemes are attractive for these measurements. The Faraday Ring Ammeter (FRA) is the first in a series of space plasma ammeters under development whose ultimate goal is detecting currents with a pA/m2 resolution. This instrument has 450 meters of twisted single mode optical fiber as its sensing element. The optics for injection (including GRIN lenses) and for coherent detection (po-larimetry) are integrated with the electronics in a (6" x 5" x 3") box. Operating at a laser wavelength of 830mn currents as small as a few hundred milliamperes through the FRA have been measured.

Nematic liquid crystals (NLCs) are anisotropic molecules which can be oriented to form uniaxial birefringent layers. NLCs aligned between suitably prepared substrates can be used as large aperture retardation plates; furthermore, the retardance of these cells can be tuned by applying an electric field. The ability to vary retardance has numerous applications in polarization control for various optical systems. Liquid crystal devices have evolved to play an important role in laser systems, displays, and optical switches. Theory, construction, performance considerations, and applications of high precision, tunable NLC retardation devices will be discussed.

A simple procedure to generate modulating left and right circular polarization states for monochromatic radiation in the far infrared and millimeter wavelengths is described. The necessary theoretical expressions to measure circular and linear dichroism using this modulator are also presented.

The measurement of light polarisation is one of the principal means of investigating the interaction of light with matter. One of the most versatile and sensitive instruments for measuring light polarisation is the photoelastic modulator (PEM), a piezoelectrically-driven device with oscillating birefringence that phase-modulates the component of a transmitted electromagnetic wave along the modulation axis. Accompanied by synchronous (phase sensitive) detection, the PEM has figured prominently in a wide range of physical measurements such as circular dichroism, for which it was initially developed', optical rotary dispersion and Faraday rotation, polarimetry of astronomical objects, and strain-induced birefringence2,3,4, ellipsometry5.

In the present article we report the results of our experiments on the possibilities of using birefringent materials for achieving spatial filtering operations. These filters divide the input spectrum into two orthogonal components and also introduce a phase difference accompanied by a shear, the nature of shear being dependent on the birefringent device used. This fact can be fruitfully utilised for a number of useful purposes, some of which are discussed in the present paper.

We report the first electrooptic depolarization (TE guided wave to TM substrate modes) modulator on Y-cut LiNb03 proton-exchanged channel waveguides operating at 632.8 nm. The depolarization scattering associated with PE planar waveguides has also been consistently observed in PE channel waveguides. The phase matching condition of this scattering is NeffiCos(0) = N_o, where Neff is the effective index of the guided mode, 0 the coherent depolarization scattering angle, and No the ordinary index of the guiding layer. All the mode indices small than No can satisfy this equation. Since the proton exchange process only increases the extraordinary index of the guiding layer the TM scattered wave will automatically goes to the substrate. In this paper we use the combination of thermal annealing and external electric field to induce the coherent depolarization scattering. Tunability of the waveguide ordinary and extraordinary indices through thermal annealing provides an alternative way to reduce the drive voltage. 13.5 dB extinction ratio is achieved with 10 volt applied voltage on a modulator with 4 μm channel width and 3 mm electrode length. The measured capacitance is 4.2 pF which gives a theoretical modulation bandwidth of 1.5 GHz.

Pitch and yaw of objects moving at high velocities can be measured with a Doppler interferometer system employing corner cube retroreflectors mounted on the moving object. Measurement of pitch or yaw alone was demonstrated in laboratory and field experiments. Using the Jones calculus, the polarization considerations for measuring both pitch and yaw simultaneously have been analyzed.

A newly developed, computer controlled experimental facility to measure two-dimensional multiple scattering of light at three different positions outside of a large cylindrical scattering volume is discussed. The light is produced by a laser beam and is incident normal to the center of the flat, top surface of the cylinder. Data acquired at all three positions, back-scatter from the top, radial-scatter at the side and transmitted through the bottom of the scattering volume, are presented. Of the three, the back-scatter and radial-scatter are discussed in more detail. In particular, comparisons are made in the measured scattered powers in the case of the incident light being linearly and circularly polarized. Preliminary experiments indicate that for both back-scatter and radial-scatter more power is detected for circularly polarized incident light than for vertically polarized. That is, in the case of light back-scattered from the top of the volume at any radial position meas-ured from the incident laser beam more power is detected when the light is circularly polarized. Similarly there is more power scattered radially for circularly polarized incident light at any position measured down from the top surface.

The development of low losses all - dielectric laser reflector is essential for powerful excimer lasers in UV and VUV. The excimer laser reflectors at wavelengths of 351nm( Xen , 308nm( XeC1) and 193nm ( ArF) consisted of Zr02 - Y203/Si0₂ and A1203/Si02 have been prepared. The reflectance in such reflectors reaches 99. 7% at wavelength of 351nm, 99. 5% at 308nm, and 98% at 193nm. And the laser in-duced damage threshold has been raised to around 8. 5J/cm2 at wavelength of 308nm.

The paper describes the architecture of a planar (N X N) optical permutation network consisting of several surface stabilized ferroelectric liquid crystals (SSFLC) sandwiched betweentwo birefringent plates at each stage. The arrangement proposed has some advantages over the permutation arrangements available in the literature.