This paper attempts to classify and illustrate with examples the techniques by which the polarization-altering properties of linear optical systems are found, and to point out some similarities of different applications.

The optimum choice of detector array and polarizing optics for an optical polarimeter is discussed.

Polarimetry within a spectral line or band is proposed as a new atmospheric remote sensor, particularly for clouds and hazes. The limitations of conventional absorption/emission spectroscopy and photopolarimetry are discussed. The selective formation and behavior of intensity and polarization lines is analyzed under a variety of atmospheric and scattering conditions. The technique, limitations and advantages of Fourier Transform Spectroscopy are reviewed as a prelude to the proposed approach. Experimental results obtained at the telescope for the planet Venus are presented as evidence for the existence, behavior and effects of line polarization. Fourier Transform Spectropolarimetry provides means for separating the effects of scattering from those of absorption, probing the internal properties of clouds and hazes, and studying the detailed wavelength dependence of polarization with variable spectral resolutions from low to high.

The Orbiter Cloud Photopolarimeter (OCPP) to be flown aboard the Pioneer Venus Orbiter spacecraft is described. This instrument, while in orbit about the planet Venus, will perform polarimetric and radiometric mapping of the Venus atmosphere in four spectral bands centered in the near ultraviolet, visible, and near infrared regions. Additionally, the instrument is equipped to provide moderate resolution imaging of the time varying cloud patterns in the near ultraviolet. In another mode of operation the instrument is capable of profiling the atmosphere at the limb of the planet to measure the particulate layering. Information resulting from these measurements is intended to provide an understanding of the global cloud dynamics and the atmospheric structure and composition on Venus. The basic operation and functional elements of the instrument are discussed. The optical configuration incorporating a polarization analyzing technique with improved accuracy is described. Long-term and short-term calibration techniques along with expected instrument performance characteristics are summarized.

A review of the use of dispersive crystal and Thomson-scattering devices as X-ray polarimeters for solar and extrasolar observations is presented. The theory, design, performance characteristics, and statistical limitations of these devices are discussed.

Several Fourier photometric ellipsometers and polarimeters are described whose operation is based on the use of modulated optical rotation. We start with the oscillating-analyzer ellipsometer (OAE) that consists of a linear analyzer preceded by an ac optical rotator and show how this basic instrument can be modified, by the temporary insertion of a quarter-wave compensator, to perform as a complete polarimeter. Permanent addition of the quarter-wave compensator and a second ac optical rotator to the OAE leads to a family of complete polarimeters in which either the compensator alone or, more generally, both the compensator and analyzer are, in effect, oscillating at the same frequency as is induced by the presence of the ac optical rotation. We show, in all cases, how the Stokes parameters of the radiation incident on the polarimeter can be determined from limited Fourier analysis of the signal output of a linear photodetector that intercepts the light leaving the polarimeter.

The design and performance of a stepping-motor driven self-nulling ellipsometer are described in detail. Three levels of instrumentation are discussed: (i) the basic instrument which has been in use in our laboratory for over ten years, (ii) the addition of a ministepping drive to provide increased resolution, and (iii) the addition of quadrature Faraday modulators to provide increased speed. It is concluded that developments in technology have made this type of instrument an inexpensive alternative to the conventional manual ellipsometer.

Modifications to standard photometric polarimeter systems that reduce measurement errors due to drift, digital noise, and stray light are described. For instruments using photo-multiplier (PM) detectors, a regulation and control circuit is discussed that also allows the linearity of the detector to be adjusted. The measured performance of a rotating-analyzer ellipsometer (RAE) using these modifications is as follows: Linearity to 5x10-4 over more than three orders of magnitude of incident light intensity, and stability to 5x10-5.

The measurement of changes in the state of polarization of light due to reflection provides an unusually sensitive tool for observing surface layers in any optically transparent environment. A fast, self-compensating ellipsometer has been used to observe the electro-chemical formation of reacted surface layers. The optical effect of mass-transport boundary layers and component imperfections have been taken into account in the interpretation of results.

In this paper we highlight the salient features of the Hughes Modulated Light Ellipsometer system including the details of the critical optical and electronic components. We present an analytical discussion of the effects of various experimental errors, including signal stability and sample alignment, on the accuracy of the system for substrate and thin-film measurements. The regions of optimum measurement accuracy deduced from these analytical studies are used as an experimental guide in the laboratory. The system has been used to study various substrates and film-substrate systems including ThF4, ZnSe, KCl, CdTe, ZnSe on KCl, and ThF4 on ZnSe. The results of these measurements are presented and discussed.

Surface anisotropy of an otherwise isotropic solid may be the result of surface contamination or surface aggregation. In the latter case, an analysis of the degree of aggregation, its depth, and the nature of the aggregates is possible by the recently developed "generalized" Maxwell Garnett Theory. In order to carry out the analysis the effective indices of refraction are needed, which can be measured accurately with the ellipsometer at different angles of incidence. Details of the analysis and examples, using some metals and silicon will be presented.

Ellipsometric measurements are affected by the electron population in surface states. This creates difficulities when studying adsorption, but also presents the experimenter with another way of studying these states. We have explored the possibility of using ellipsometry to study the electronic surface structure of silver iodide by making the ellipsometric measurements at one unchanging wavelength while illuminating the film with light of varying wavelength and observing the resulting changes in the ellipsometric parameters. Previous ellipsometric studies of surface states have not made use of the second light source. Our results indicate that this method is practical and also indicate that care must be taken when using ellipsometry to study adsorption reactions when other light sources also illuminate the surface.

Ellipsometric measurements at 5461 Å on etched and mechanically polished samples of KC1 are reported. The results show that (1) etched KC1 has a refractive index nearly equal to the bulk value (1.49); (2) polished KC1 samples have a damaged surface layer with indices of 1.42 to 1.45, but there is an ambiguity in the thickness of this layer; and (3) the difference in refractive index between the bulk and surface values has a positive correlation with the increase in total absorption at 10.6 μm measured for the sample. Preliminary measurements on polished CaF2 are also given.

The Antireflection-coated Metal Oxide Semiconductor (AMOS) solar cell is an attractive candidate for converting solar energy to electrical energy for space and terrestrial applications because of its simplicity, high solar-energy conversion efficiency (15%), and adaptability to low-cost thin-film structure, when the semiconductor is made of direct bandgap material. The high energy conversion efficiency of the AMOS cell is partially due to its relatively good minority carrier collection efficiency and, hence, good current out-put, when a direct bandgap material like GaAs is used. Obviously, the amount of sunlight which can be coupled into the solar cell must be maximized by a suitable antireflection (AR) coating. In this paper, comprehensive methods for obtaining parameters of an optimum single-layer AR coating on an AMOS solar cell to match the entire sunlight spectrum, rather than a single wavelength, will be given. In this method, therefore, the effects of a solar spectrum, spectral response of the solar cell and optical properties of the solar cell are collectively considered.

An automated interpretation of ellipsometer measurements of anodic film growth, which takes electrical charge passed and mass transport in the electrolyte into account, has been developed. The optical model assumes the existence of a homogeneous solid film, covered by two inhomogeneous layers in the liquid phase. A computer program finds a least-squares fit in seven-dimensional space.

The polarizing microscope has been used to reveal submicroscopic organization in biological materials for over a century. Examples of intrinsic, form, stress and anomalous dispersion birefringence have all been found, sometimes in the same cell. A major advantage of birefringence analysis is that cells can be studied in their native state. Also, structural gradients can sometimes be seen within a cell that are not detected using other physical or anatomical methods. On the other hand, the technique is non-specific, so experiments must be carefully designed to extract information about molecular level organization. Our current insight into the structure of biological membranes had its beginnings in birefringence analyses of the multi-membrane layers found in myelin sheaths and retinal rod outer segments. Recent studies of rod outer segments have shown that the internal ordering of membrane components can change as the membrane ages. Since birefringence can be monitored in viable cells, the technique has been applied to a variety of excitable tissues. Membrane-potential dependent structure changes have been found in nerve and muscle. In rod outer segments, complex birefringence changes are initiated when light is absorbed by visual pigments. Birefringence studies may therefore eventually provide insights into membrane function as well as structure.

The theory and observed characteristics of magneto-optical rotation (MOR) and magnetic circular dichroism (MCD) are described. They are then related to applications in optical instrumentation, and in the determination of atomic and molecular structure. Special emphasis is given to the use of lasers in improving the measurement of these magneto-optic effects. It is suggested that high-resolution laser spectroscopy will replace MCD measurements in some applications.

Recent advances in our vibrational circular dichroism (VCD) instumentation are described. A new CaF2 photoelastic modulator and a xenon lamp have been incorporated into the VCD spectrometer. These changes have substantially increased the sensitivity and extended the long wavelength range of the instrument. Some examples of VCD spectra obtained with the improved instrumentation are presented and future developments that will further increase both sensitivity and wavelength range are discussed.

A sensitive spectrometer for the measurement of circular polarization of emission, utilizing a photoelastic modulator, is presented. This spectrometer, when augmented by a superconducting magnet and dewar assembly, provides an excellent system for studying magnetically induced circular polarization of emission (MICE). In order to exemplify both the system and the usefulness of MICE, a partial analysis of the MICE observed from Ru(4,7- dipheny1-1,10-phenanthroline)3C12 dispersed in a polymethylmethacrylate (PMM) matrix in the 2 to 100°K temperature range is reported. Also presented is a discussion of the effects of photoselection on the observed MICE for these D3 symmetry complexes. It is found that MICE is more sensitive to the detailed nature of the levels involved in emission than a combination of zero field techniques. MICE should prove to be an exceptionally useful tool for probing excited states of inorganic complexes.

By summing the rotational strength moments, R(q) = Σn(En-Eo)q R-on M-no (q=0...6), over all transitions in an optically active molecule one may obtain expressions explicitly dependent upon nuclear geometry, atomic charges, and local atomic anisotropy. In this work the resulting terms are analysed and ultimately applied to individual transitions as well as dispersion. In the framework of SCF molecular orbital theory coupled oscillator, local atomic orbital distortion, and inherent dissymmetry contributions are identified and their relative magnitudes estimated. A significant conclusion reached is that if the SCF orbitals can be localized, then the traditional correlation expressions are qualitatively correct for the dispersion, while both SCF ( independent electron) and CI (coupled oscillator) terms are often of equal importance for individual transitions.

Ferrous chloride is an antiferromagnet (AF) below its Neel temperature TN, but it may be driven into a saturated paramagnetic (SP) state by an external magnetic field applied along the c-axis. This AF-SP transition is first order below and continuous above a tricritical temperature Tc, a classic example of metamagnetism. With a pulsed dye laser, piezoelectric modulator, and a unique gated amplifier, we monitored the scattering of circularly polarized light by the mixed AF-SP phase below Tc. Above Tc the optical density of a sharp absorption line changes with the spin ordering; because the transition couples to spin fluctuations, the optical density maximizes in the SP phase. We have used these optical techniques to map the thermodynamic phase diagrams of FeC12 and FeC12 doped with cadmium, which to our knowledge is the first study of a randomly disordered critical system.

We have developed an instrument which permits the direct measurement of all sixteen elements of the 4 x 4 phase matrix. This is accomplished using four electro-optic modulators to modulate the polarization of the incident and scattered light. Synchronous detection is then used to measure each of the sixteen individual matrix elements. The instrument and brief theory of its operation will be discussed, along with possible applications.

There has been in recent years an ever increasing need for a fast determination of particle size distribution in systems where the distribution changes with time so much that the conventional methods are not applicable unless one sacrifices significantly precision of the result obtained. In our laboratory the possibility was explored of obtaining distribution curves by determining exclusively the angular location of scattering extrema, i.e. maxima and minima. Several possible methods of procedure were found to be promising. One of these is being described in the following. On using a minicomputer in which one stores that part of the information available from Tables just issued, which is applicable to a given system, the size distribution should be obtainable within less than five minutes including the time needed for angular location of extrema.

The polarization of reflected radiation can provide useful information which could be used in remote sensing applications to help distinguish different natural surfaces with similar spectral signatures. Yet the use of polarization has been almost completely neglected in remote sensing applications partially because of the lack of understanding of the information contained in the polarization field. In this paper, examples of the polarization of natural scenes will be presented and the information contained in the polarization field will be discussed. The imagery presented was collected by taking sets of four photographs of various natural scenes using a polarizing filter to detect the polarization field. The polarization field was analyzed by digitizing the photographs and processing the results at the Image Processing Laboratory on the Berkeley campus of the University of California.

Reflection polarimetry is a remote-sensing tool sensitive to the refractive index and microtexture of solid surfaces. Mechanisms producing linear polarization within a rough, porous, or particulate surface are discussed, and laboratory techniques for precise measurements are described in some detail. Polarimetry of atmosphereless solar-system bodies provides valuable indications of albedo for objects too small and distant for direct diameter determinations, and reveals that even quite small asteroids and satellites have particulate surfaces.

A high altitude balloon carrying four optical instruments was flown on March 17, 1976, from Holloman Air Force Base, New Mexico. A modified spacecraft scanning radiometer (NIMBUS /EARTH RADIATION BUDGET EXPERIMENT) measured the linear polarization properties of reflected sunlight in broad intervals of the visible and near-infrared spectrum. The instrument scanned from horizon to horizon in the principal plane of the sun as the balloon ascended to float altitude of 37 km. The instrument and its calibration will be described. Plots of the intensity, plane and degree of linear polarization will be used with coincident photographs to examine the effects of the earth's surface and atmosphere on polarization.

In an effort to develop an index of atmospheric turbidity, measurements of the polarization and intensity of light from the sunlit sky were made at the South Pole station, Antarctica. Preliminary data from these measurements at wavelengths of 0.398 and 0.70 μm taken in the vertical plane through the sun are shown and compared with similar data computed for a pure molecular atmosphere overlying a highly reflecting Lambert type surface. The general features of the measured fields are similar to those of the theoretical model, but some consistent discrepancies exist for both the intensity and degree of polarization. It is suggested that the discrepancies are probably due to the fact that a Lambert type surface is not a good approximation to the actual snow surface which exists at the South Pole.

Scattering properties of mono- and polydisperse mixtures of randomly oriented rough spheres, cubes, octahedrons, and irregular particles are compared with Mie-calculations for smooth spheres of equal volume. Correspondence in the forward direction, as far as measured, is quite good for dielectric and absorbing materials, as well, whereas dominant differences occur at medium scattering angles and towards backscattering. Polarization properties of nonspherical particles are different from those of spheres, too, especially for non-absorbing materials. Additionally cross polarizing properties of irregular particles are discussed.

The direction, but not the magnitude, of the solar coronal magnetic field is encoded in the linear polarization of certain coronal emission lines. The High Altitude Observatory, in collaboration with the Sacramento Peak Observatory, has constructed a polarimeter which measures the plane polarization of the 10747A and 10798A Fe XIII emission lines. The instrument simultaneously provides similar measurements of the continuum corona and the sky at 10690A to give the net emission line intensity and polarization. Polarization brightness maps made with the 10747A line clearly show the large scale organization of the coronal magnetic field and signatures characteristic of diverging fields over sunspots, horizontal fields above filament channels, and the Van Vleck turnover in helmet streamers.

A photoelectric polarimeter for measuring solar spectral line profiles in all four Stokes parameters has been built and operates on a 40 cm coronagraph in a joint project with Sacramento Peak Observatory. A description of the optical and electronic systems and the calibration scheme is presented. Performance parameters determined from observations are also given. The polarimeter package consisting of a pair of KDP's, a quarter wave plate, and a polarizing beam splitter is located at the prime focus of the coronograph. Modulation of the KDP's encodes polarization information into intensity signals that are electronically detected. The scanning of the spectrum, accomplished by rotating the grating, permits Stokes line profiles to be recorded on magnetic tape for processing. The instrument can be used to scan any line from 3900 to 7000Å with a spectral resolution of .01Å. Polarizations as small as .001 percent are detectable. The polarimeter and observing system are computer controlled.

An astronomical polarimeter is described that uses a photoelastic modulator and digital synchronous detection to measure simultaneously three of the four Stokes' parameters of the incident light. Light polarization by the telescope optics is the only important source of systematic offset error. In a stand-alone portable version a minicomputer is employed for data handling, control, and quick-look Fourier trans-formation of time-series data. A second version being developed for the new Anglo-French telescope interfaces to the telescope's data-handling computer via CAMAC. Results of recent observational programs on the x-ray binary star AM Herculis and atmospheric aerosol are shown to illustrate the instrument's capabilities.