This special issue of Optical Engineering contains 13 papers surveying polarization considerations for optical systems. Papers representing the thin film, solar astronomy, optical design, optical data storage, and optical communications communities are included, attesting to the broad interest in polarization issues.

A ray representing a vector wave is traced through an optical system. The electric field perpendicular to the (ray) direction of propagation is represented by a Jones vector. At each surface the results of a thin-film calculation are used to form a "surface" Jones matrix. For a given ray, a product of surface Jones matrices forms an "instrumental" ray matrix. Coordinate frames and sign conventions are emphasized.

For most optical systems it is typically assumed that the transmitted wavefront has uniform for Gaussian) amplitude and constant polarization state. This is the default assumption of geometrical optics. This paper considers methods suitable for analyzing systems for which this assumption is not valid. Such methods of polarization analysis include polarization ray tracing and polarization aberration theory. Definitions of the basic classes of polarization phenomena and a review of the Jones calculus are included to form a basis for the discussion.

Polarization aberrations are variations of the polarization associated with different ray paths through an optical system. This paper presents particular polarization aberration expansion that is second order in the object and pupil coordinates and describes polarization effects that are functionally equivalent to the wavefront aberration terms: piston, tilt, and defocus. This polarization aberration expansion is applicable to weakly polarizing systems, such as radially symmetric systems of lenses and coatings, as well as to strongly polarizing systems incorporating polarizers and retarders. A computer simulation of this expansion has been performed, and graphical results are presented displaying the effect of 24 of these polarization aberrations acting on linearly and circularly polarized light.

Corrective procedures have been undertaken that will permit quantitative polarimetry using the 75 cm Sacramento Peak Vacuum Tower Telescope. A new vacuum entrance window provides an improvement in the spatial uniformity of the polarization effect over the old strongly stressed window of almost two orders of magnitude. Even though the intrinsic spatial variation of the polarization effect is less than 5 x 10-4, a constant residual birefringence in the vacuum entrance and exit windows and 45° mirror reflections introduces a uniform retardance that is as large as 1/8 wave and is a function of the telescope pointing parameters. However, a particular sampling of input polarization states and corresponding measurements of the output polarization states determines uniquely the matrix of a serial system consisting of n spatially uniform, nonscattering, rotatable, nonsingular polarization modification elements. A numerical method is given for inverting measurements taken in a way that did not strictly conform to the nominal sampling. The method was applied to polarization measurements obtained with the National Solar Observatory polarimeter mounted at the prime focus of the Vacuum Tower Telescope over the course of a day as the telescope pointing changed to track the sun. The resulting matrix model for the telescope is a function of its three pointing parameters and is applicable for telescope pointing to all sky angles. The accuracy of the present model, 2.5%, is limited by the quality of the polarimeter calibration and by simplifying assumptions.

The operation of a photoelastic modulator (PEM) type ellipsometer is described in terms of Mueller matrix elements. The phase shift (5 and the relative amplitude attenuation ratio tan * between orthogonal polarization components are contained in the Mueller matrix elements and can be obtained through combinations of measured matrix elements. A phase shift measurement accuracy of ±0.2° has been obtained without calibration. A computer-controlled implementation is described along with simple algorithms to extract the ellipsometric constants. The Mueller matrix of a magneto-optic (MO) film medium system has been used along with the Mueller matrix for a "leaky" beamsplitter to form the Mueller matrix for an ideal MO read-back system. One of the Stokes parameters is proportional to the differential detection signal commonly used in MO data detection schemes.

This paper treats the fundamentals of infrared spectropolarimetry as a step in understanding electro-optical materials and designing better spatial light modulators. It describes the issues in converting a Fourier transform spectrometer to perform spectropolarimetric measurements and includes mathematics to interpret the resulting spectropolarimetric data. Two distinct differences exist between this proposed instrumentation and previous infrared crystal optics studies: (1) this instrument acquires data simultaneously at all wavelengths within its spectral range and (2) it measures Mueller polarization matrices. Conventional measure-ments with laser polarimeters take birefringence data with applied fields at a few laser wavelengths. With the spectropolarimeter, data are obtained over the entire spectrum, including on and near absorption bands where the most interesting phenomena occur. Measuring Mueller matrices as a function of wavelength provides data on polarization and scattering, effects that will ultimately limit the performance of a modulating crystal. Thus, more data are available with which to compare materials and optimize modulator designs. Better modulators must result from such investigations.

A general polarimeter for the precise measurement of Stokes intensities was developed and was used for testing the Sacramento Peak Vacuum Tower Telescope and other optical instrumentation. The design is based upon the polarimeter described by F. Orrall [Solar Magnetic Fields, IAU (1971)] and M. Makita et al. [Ann. Tokyo Astron. Obs. 19 (1982)], with some simplifications. A control computer sets parameters in the integration electronics and provides simple readout for an experiment control or analysis computer. Calibration of the polarimeter is defined by a Mueller matrix for the system; the calibration matrix compensates for the systematics of the polarimeter. The calibration matrix was derived using an optical wheel containing many orientations of sheet polarizers, partial polarizers, and insertable wave plates. The rms of the calibration solution is about 0.6%. The calibration procedure as it is presently defined limits the accuracy of the polarimeter.

In a study by the Marshall Space Flight Center (MSFC) for the Air Force Geophysics Laboratory (AFGL), a design concept was developed for a polarimeter on the vector magnetograph of the SAMEX satellite (Solar Activity Measurements Experiments) that would be very sensitive to solar vector magnetic fields. To provide an understanding of how the polarimeter design was selected, a description of the Poincare sphere is presented, along with the instrument scientific requirements. The Poincare sphere is used as a visual technique in describing various polarimeters and the systematic errors associated with them. Analysis of the polarimeter designs to minimize crosstalk between incident circularly polarized light and the linear polarization measurement is stressed. After a polarimeter design is selected, the calibration techniques to determine the systematic errors in the "perfect" polarimeter are discussed.

An optical design and polarization analysis of the Air Force/NASA Solar Activity Measurements Experiments solar vector magnetograph optical system is performed. Polarization aberration theory demonstrates that conventional telescope coating designs introduce unacceptably high levels of polarization aberrations into the optical system. Several ultralow polarization mirror and lens coatings designs for this instrument are discussed. Balancing of polarization aberrations at different surfaces is demonstrated.

The polarization matching mixer (U.S. Patent No. 4,723,315) is a device that uses polarization beamsplitters to first combine local oscillator and signal light beams into an orthogonal-polarization mixed beam and then split this beam into two matched-polarization mixed beams ideally suited for differential detection. It has potential advantages for coherent communications systems since it offers improvements in optical efficiency through sensing and controlling the polarization state of the incoming signal beam in the receiver. In multiple-wavelength laser diode systems, it may make it possible to increase the number of channels used within a given wavelength band by allowing fine pointing, polarization, and wavelength sensing through diffraction grating dispersers. This paper discusses the polarization matching mixer, how it works, how it compares to the use of amplitude beamsplitters, and how it can be used to reduce signal loss due to degradation in signal polarization. Its potential application to multiple-wavelength laser diode systems is briefly discussed. The paper closes with a discussion of high efficiency polarization beamsplitters.

Grating, and hence spectrograph efficiency, can be a strong function of the polarization of incident light. A polarization device has been designed to divide the light entering a spectrograph into two orthogonal polarizations, one of which is then rotated 90°, so that all of the light incident on the grating is polarized either parallel to or perpendicular to the grating grooves. Spectrograph throughput is thereby im-proved while also becoming independent of input polarization. Tests at the coude spectrograph of the Canada-France-Hawaii Telescope with an 830 f/mm grating revealed a 28% improvement in spectrograph throughput at a wavelength of 500 nm.

This study demonstrates how lateral scattering is affected by particle distribution and by optical depth, in the direction of the incident linearly polarized light. Previous publications have linked only scattering particle size to lateral scattering anisotropy. This presentation indicates that the anisotropy apparently disappears for optical depths of approximately 10 and greater if the scattering is produced by uniformly sized particles. In addition, for at least one particle distribution (latex paint in water), this anisotropy does not appear regardless of the optical depth.

Optical beamsplitters often consist of repeated pairs of high and low index quarter-wave layers. At oblique angles of incidence, such coatings typically have a fairly high polarization ratio. Reflectance, transmittance, and phase for the two orthogonal planes of polarization, s and p, are different in general. Here, we present the results of the design of all-dielectric beamsplitter coatings with very low polarization ratios. An initial sinusoidal refractive index profile, optimized with a refining computer program, yields a 50±1% beamsplitter in the 450 to 650 nm wavelength range, with less than 0.5% (abs.) difference between the s and p reflectance in most of this interval. Matching the elements of the characteristic matrix of this design with those of a generic homogeneous multilayer stack yields the starting design A(HL)7HS for a reflectance to transmittance ratio of R:T = 50:50% and 30:70% beamsplitters, which are optimized for the 500 to 600 nm wavelength range and angles of incidence of 40°, 50°, and 60° using a computer program based on a damped least squares refining technique. The average deviation from the nominal beamsplitting ratio is less than 0.5% for all given design examples. The maximum deviations are about 2% in this wavelength range.

A CO2 waveguide laser with programmable pulse profile, intended for use in coherent laser radar applications, has been designed and characterized. Gain and intracavity losses were measured and compared with known component losses and theoretical mode coupling efficiencies. A set of coupled rate equations was used for calculating the peak power. Input parameters in those calculations were the measured gain and loss together with published data on population relaxation. The observed Q-switched pulse was in reasonable agreement with the calculated pulse form. Average power and peak power could be fitted to simple empirical formulas. Q-switched and cavity-dumped pulses with a pulse length of 13 ns were demonstrated, limited only by the pulse generator. The pulse length is ultimately limited by the cavity round-trip time.

The calibration of the Halogen Occultation Experiment (HALOE) sun sensor is described. This system consists of two energy-balancing silicon detectors to provide coarse azimuth and elevation control signals and a silicon photodiode array to provide top and bottom solar edge data for fine elevation control. All three detectors were calibrated on a mountaintop near Tucson, Ariz., using the Langley plot technique. The conventional Langley plot technique was modified to allow calibration of the two coarse detectors, which operate wideband. A brief description of the test setup is given. The HALOE instrument is a gas correlation radiometer that is now being developed for the Upper Atmospheric Research Satellite. A significant part of the paper includes other key features of the instrument for completeness of the subject.

In optical interferometers alteration of the pathlength is usually achieved by moving one of the two interferometer mirrors back and forth. Through the use of rotating retroreflectors (corner reflectors), two slightly different concepts have been developed to replace this stop-and-go movement by a continuous rotation.

Using the rainbow effect, produced by using a white light source in the reconstruction process of an image hologram, it is possible to obtain normal color two-dimensional images. The technique described in this work requires the recording of three holograms on the same plate, using laser light of a single wavelength (He-Ne laser, A = 632.8 nm) with three reference beams, each at a different angle. The color separation technique of Gale and Knop [Appl. Opt. 15(19), 2189-2198 (1976)] was used to obtain three black-and-white transparencies from one color transparency. The holographic image can be observed when the hologram is illuminated with a white light source. The experimental setup and the conditions for obtaining original color objects are discussed.

Solid-state imaging devices are increasingly replacing conventional photographic techniques in many fields. This paper describes a high speed camera that makes use of two special features of the frame-transfer CCD imager, namely, its simultaneous integration process and the subsequent shifting of the charge distribution into the storage register. Details of the system and its application in the investigation of disintegrating liquid jets are given.

As I indicated in my editorial in the May 1986 issue of Optical Engineering, "special issues" have been the backbone of the journal for a great many years. A "special issue" is one in which a majority of the papers are devoted to one or two "special" topics related to the field of optical engineering. In both 1986 and 1987, nine of the 12 journal issues were special issues, and in 1988 there were eight special issues. We currently have seven special issues scheduled for 1989, although that number could vary up or down by one depending on circumstances.

This book constitutes the final report of the European Joint Optical Bistability Project (EJOB) under the European Communities Stimulation of Science and Technology research program. The project involved eight participating and ten associate universities distributed within the European community in the United Kingdom, Belgium, West Germany, France, and Italy and was funded at the level of 1.8 million European Common Market Units (ECU) over a period of two year beginning at the end of 1983.