The physics of polarized light is discussed in textbooks and will not be repeated in this talk. Instead, the talk will illustrate with many demonstrations that the methods of polarized light are easy and yet lend themselves to extremely sensitive observations and precise measurements.
Various types of instruments capable of giving a complete polarization state measurement are reviewed. Included are those which employ adjustable combinations of a retarder and analyzer, continuously rotating elements, polarization-modulating elements, and interferometry. General comments are made regarding precision and accuracy, and specific comparisons are made on the basis of speed, ease of data reduction, spectral regions and range, and amenability to computer control. Applications of polarimeters are also reviewed briefly. They fall into two categories, depending on whether the light is supplied by the instrument or comes from outside the instrument; they include astronomical measurements, characterization of light sources, and the measurement of the polarization-altering properties (including depolarization) of optical systems.
We derive the equations that permit the use of six different periodic analyzers for the frequency-mixing detection (FMD) of polarization-modulated light. The six periodic analyzers are (1) the rotating linear analyzer, (2) rotating half-wave plate and fixed linear analyzer, (3) rotating quarter-wave plate and fixed linear analyzer, (4) rotating linear analyzer and fixed linear analyzer, (5) oscillating-phase retarder and fixed linear analyzer, and (6) oscillating optical rotator and fixed linear analyzer. In all cases, the quiescent (average) polarization and the polarization- and intensity- modulation parameters of the beam can be easily and explicitly determined from limited Fourier analysis of the detected signal.
The design and performance of a new automatic ellipsometer is described. The instrument is of the balancing or null-seeking type, using Faraday modulators to detect out-of-balance conditions, stepper motors to drive the polarizing and analyzing prisms, and Moire fringe counters to measure the angles of the prisms.
In the past several years important developments have been made in the construction and theory of birefringent filters. Tunable filters that operate from 4500-7000 Å with full widths at half maximum of .05 Å and maximum transmissions of almost 20 percent have been constructed. Inexpensive large aperture (≥15 cm) achromatic waveplates have been fabricated that allow full use of the resolution-solid angle products 102 that of Fabry-Perots and 104 that of grating systems have been constructed.
Large glass laser systems used in laser fusion research operate with intrasystem power densities of up to 1010 W/cm2. These multibeam laser systems utilize numerous subassemblies to perform various tasks. Polarization components are important elements in subassemblies such as unidirectional optical isolators, bidirectional optical isolators and variable ratio beam dividers. At power densities of gigawatts/cm2, nonlinear effects limit the power level that can be prieagatV through a glass laser system. An intensity induced refractive index change of PPM at levels of 1010 w/cm2 can cause whole beam self-focusing and small scale beam break-up. Polarization components for use in these systems must be selected on the basis of minimal contribution to nonlinear phenomena as well as acceptable optical performance. Nonlinear considerations exclude the use of such components as birefringent crystal polarizers and the MacNeille polarizer in the presence of gigawatt/cm power densities. Thin film plate polarizers are used in large aperture low contrast applications because they combine acceptable optical performance with a relatively low nonlinear contribution. This review paper describes some commonly used polarization components and discusses their applicability to high power glass laser systems.
The states of polarization of the output beam (632.8 nm) of internal mirror He-Ne lasers have been investigated using a scanning Fabry-Perot Interferometer and linear polarizers. It was found that during the initial warmup period of the laser, the output power fluctuates periodically and the axial modes sweep rapidly across the Doppler gain profile. A thermal analysis shows that the sweeping rate is in good agreement with the calculated rate of expansion of the laser cavity. During certain periods of time which recur with a frequency that is related to the mode motion the output beam is linearly polarized in two preferred orthogonal directions. The states of polarization of the output beam are due to the tendency of axial modes to be linearly polarized, with an orthogonal relationship existing at times between adjacent modes. However, the polarization states of the total beam and of the individual modes also vary periodically and in a complicated manner as the laser warms up. It was found that the simple description of orthogonally polarized alternate modes is inadequate to characterize the beam during a large fraction of the time corresponding to a fluctuation cycle. The implications of these polarization properties on laser scanning applications are discussed.
Dichroic iodine polarizers with light transmissions over 50 percent approach the critical range of applicability in Liquid Crystal Displays (LCD) because of fading and polarization loss on environmental exposure. This degradation and the development of edge bubbles with adhered polarizers are two of the major problems encountered in constructing the display. The manufacture and properties of LCD polarizers are described in order to understand the sources of and solutions to these problems. Other required properties, such as UV resistance, heat and chemical stability are obtained by proper material selection and rigorously controlled manufacturing conditions. Selection of adhesives for bonding polarizing elements to the LCD cell is critical as the adhesive can become the major factor in determining the life of the polarizer. Accelerated environmental exposure of several commercially available adhesive systems indicates a wide range of stability.
PLZT electrooptic shutters utilized as thermal/flash protective devices (TFPD) are currently under development by Sandia Laboratories for the USAF Life Support System Program Office at Wright Patterson Air Force Base, Ohio and the U. S. Army Natick Laboratories, Natick, Massachusetts. The PLZT/TFPD is being developed to provide protection for aircrews and vehicle operators from temporary flashblindness effects and permanent retinal burns which may result from exposure to the brilliant flash of a nuclear detonation. The operational characteristics of PLZT electrooptic shutters is briefly described, and several applications are presented. Some of the recent developments in PLZT electro-optic shutter design are also described, with emphasis on a new approach for applying interdigital electrodes to polished PLZT wafers, techniques for bonding and mounting PLZT lens assemblies, and recent improvements in the efficiency of sheet polarizers.
A great deal of information can be obtained about aerosol and Rayleigh scattering by observing the polarization state for both reflected and transmitted radiation. Results of neutral point behavior are presented for 1) a Rayleigh or molecular scattering atmosphere; 2) a haze L distribution of aerosols typical of those found in the earth's atmosphere; and 3) two actual models of the earth's atmosphere which carbine Rayleigh scattering with a normal aerosol content and with a one-third normal aerosol content.
Some uses of polarized light in optical spectroscopy are summarized. The application of modulation techniques to the study of linear and circular dichroism is discussed. The advantages and disadvantages of currently available electro-optic and photoelastic modulators for phase modulation of light are surveyed. An example of a new phenomenon - vibrational circular dichroism - rendered observable by the development of the photoelastic modulator is presented.
An overview of materials research, utilizing the unique power of polarized light for the optical characterization of materials is presented. For ease of discussion, the article is divided into two parts as characterization of materials (a) in their natural state and (b) under the influence of external stresses.
Several significant applications of ellipsometry in monitoring certain molecular and cellular biological processes in vitro are reviewed. The applications are derived from the important fields of blood coagulation, immunology, cytobiology and cytopathology.
Polarization modulation of light from a 633 nm He-Ne laser, using the Pockels and Faraday effects in appropriate materials, can serve as an electrometer and magnetometer with sensitivities to 0.06 volt/cm and 0.03 gauss or better. With the sensor material placed in the field and the laser illuminator and receiver mounted remotely, this technique can be used for precise, wideband measurement of transient effects and power flow in substation environments where high fields prohibit direct measurements. This paper describes the performance of these devices used in prototype systems for voltage transient monitoring and also for precise voltage and current metering. The latter system requires thermal sensing as well, with an accuracy of 0.1°C; optical methods for accomplishing this will be described.
Some applications of polarized light in holography and optical information processing are reviewed. The holographic applications include polarization contrast, image subtraction, color interferometry and the study of photoelasticity. In optical information processing the applications discussed are real-time optical modulators, photodichroic crystals, Vectograph film, superresolution, polarization gratings and polarization interferometers. Each application is presented in sufficient detail to clearly illustrate how the properties of polarized light are utilized.
Linear dichroic filters polarize electromagnetic radiation by anisotropic absorption. This paper describes the general characteristics of these dichroic polarizers and discusses some of their applications. Spectral data are presented for dichroic polarizers for the near ultraviolet, the visible (neutral and colored) and the near infrared regions.
After a brief review of the published literature on the effect of pressure on the conformation of macromolecules, the advantage of using the technique of Optical Rotatory Dispersion (ORD) in such studies is brought out. An experimental design to carry out such ORD measurements at high pressure is presented.
Photoresist has been extensively used in the semiconductor industry for the masking and etching operation of integrated circuit fabrication. Photoresist cleanliness is a major factor influencing the overall quality of the photolithographic process. Because of its high sensitivity and the non-destructive nature of optical measurements, ellipsometry has been used in the present study to characterize thin residual films on thermally oxidized silicon. The optical constants of silicon and refractive index and thickness of the oxide film have been determined ellipsometrically at λ6328Å. Thin residual films of less than 50Å resulted as determined by the difference in the measurements before and after a given photolithographic process. Sample results are presented to show that ellipsometry is an extremely sensitive and effective tool of monitoring the cleanliness of photoresist treated surface after photolithographic process. Because of the limited precision and accuracy of our present ellipsometer, the optical constants of such a very thin residual film cannot be determined precisely.