William L. Wolfe

Refractive indexes and temperature coefficients of germanium and silicon

The refractive indexes and their variations with temperature for silicon and germanium have been measured over the 95-298-K and 2.5-12-microm ranges. Data are given for the refractive index that are in reasonable agreement with those of previous investigators. For dn/dT the values are independent of wavelength and are approximately 1.5 x 10(-4) (K)(-1) and 4.0 x 10(-4) (K)(-1) for silicon and germanium, respectively.

Light-scattering models for spheres on a conducting plane: comparison with experiment

Three models have been developed to describe light scattering from a sphere in contact with a mirror. With two of the models the mirror was replaced with an image sphere. Light scattering from each sphere is assumed to follow the Mie theory: no further interaction between the sphere and mirror is assumed. The models differ in their consideration of the interaction of scattered fields from the spheres. The results of the models are compared to experimental values obtained for polystyrene spheres, 0.984 microm in diameter, with incident radiation lambda= 0.6328 and 0.4416 microm. The comparison indicates that a best fit can be obtained by assuming that the real sphere and its image sphere are coherent light sources with a phase difference of pi.

Scattering from a small sphere near a surface

We examine four theories that predict the scattered radiation from a system composed of a small sphere and a plane and show that in the far field the scattering amplitude components predicted by these theories are essentially the same. We express the scattering intensities in Mueller matrix representation and examine the far-field Mueller matrix as a function of various parameters.

The Theory And Measurement Of Bidirectional Reflectance Distribution Function (Brdf) And Bidirectional Transmittance Distribution Function (BTDF)

The concepts of BRDF (Bidirectional Reflectance Distribution Function) and BTDF (Bidirectional Transmittance Distribution Function) are defined and discussed as being the ratios of differential outputs of radiance divided by differential inputs of irradiance. Appropriate measurement arrangements and procedures are presented, and the problems are described that are involved in going from the differentials of theory to the finite quantities of measurement. Finally appropriate data reduction schemes are given for determining BRDF and BTDF from these measurements.

Scattering from microrough surfaces: comparison of theory and experiment

Scattering data taken at 0.6328, 3.39, and 10.6 μm are compared with theoretical calculations based on vector and scalar theories of scattering. Methods are described for obtaining the rms surface height using various degrees of dependence on the models of scattering.

Light scattering Mueller matrix for a surface contaminated by a single particle in the Rayleigh limit

A ray-tracing model was used to derive the light scattering Mueller matrix element curves for a dipole near a perfect surface as a function of incident angle, scattering angle, and surface refractive index. This system represents a fundamental system composed of a perfect plane surface and a perfect (Rayleigh) scatterer.

Scatter from particulate-contaminated mirrors. part 1: theory and experiment for polystyrene spheres and λ=0.6328 μm

The scattered light resulting from polystyrene spheres residing on mirrors was measured at λ = 0.6328 μm, and results are compared to that predicted by a modified Mie theory. The method for cleaning the samples, counting and measuring particles, the measurement procedure, and the theoretical model employed to predict the scatter from contaminants on mirrors are discussed. The comparisons between theory and experiment indicate that the theory predicts the forward scatter, but the backscatter predictions are not as successful. The indication is that the developed model can accurately predict the scatter from dust on mirrors.

Technique for measuring the refractive index and its change with temperature in the infrared

A simple method for measuring refractive index in the infrared is described. It uses autocollimation from the front surface of a prism and requires only that the receiver be moved to measure a new deviated ray when either the wavelength of the source or the temperature of the sample is changed. An error analysis that includes consideration of the evacuated sample space and wedge in the chamber windows shows that errors as low as one part in the fourth decimal place can be obtained.

Cavity radiators: an ecumenical theory

Multiple reflection considerations give cavity emissivity as an infinite series of nested integrals. The Liou-ville-Neumann series solution to the Fredholm integral equation of the second kind gives the same series for integral equation formulation of the cavity problem when the walls are gray, Lambertian, and isothermal. A compact solution, derived from the series, stimulates interesting comparisons among the multiple reflection analyses of Gouffé, De Vos, Treuenfels, Kelly, and Bartell and Wolfe and the integral equation theories of Sparrow, Albers, and Eckert; Sparrow and Jonsson; Syndor; Bedford and Ma; and Chandos and Chandos.

Cryogenic refractive indices and temperature coefficients of cadmium telluride from 6 μm to 22 μm

The index of refraction and its variation with wavelength and temperature were measured for cadmium telluride made by chemical vapor deposition (CVD). The measurement at 20 K using liquid helium as coolant is reported for the first time. The refractive index at 10 microm and 20 K is 2.6466, and the average temperature coefficient at 10 microm and in the range 20-80 K is 4.9 x 10(-5)/K.