Engineering topics
Publications and source records attributed to Wang, Yaujen.
Report describes experimental investigation of far-field diffracton by normally illuminated circular apertures with diameters of several wavelengths of incident light. Purpose of investigation to determine whether Keller's "geometrical" theory of diffraction valid for diffraction phenomena of this kind.
A modified Twyman-Green interferometer is in use that makes possible wavefront testing of optical filters at any wavelength from 200 to 1100 nanometers. The use of mirrors for collimation and pupil imaging makes the intrument achromatic, and therefore the focus is fixed over the entire bandwidth.
Mathematical model of scattering expanded from visible to include infrared wavelengths. Paper describes extension of mathematical model of scattering from mirror slightly contaminated with particulates. Original version of model applies to scattering at visible wavelengths. Updated version used to predict scattering at wavelengths from visible through infrared, based on measurements in visible spectrum.
Additional terms account for effects of particulate contamination. Semiempirical mathematical model of scattering of light from surface of mirror gives improved account of effects of particulate contamination. Models that treated only scattering by microscopic irregularities in surface gave bidirectional reflectance distribution functions differing from measured scattering intensities over some ranges of angles.
This paper presents a derivation of a simplified analytical solution of diffraction from a Lyot (1939) system designed for observation of the solar corona outside of eclipses. Applying the theorem of Papoulis (1986) to simplify the calculations, a simplified solution is derived which is found to be in reasonable agreement with the exact solution. The simplified solution suffices for the preliminary evaluation of the amount of diffraction reduction needed to meet certain system requirements and also serves as a guideline for further apodization.
A model has been used to fit the bidirectional reflectance distribution function for a variety of samples with different angles of incidence and degrees of contamination and roughness by the proper adjustment of six parameters. Exponential and Gaussian composite surface height autocorrelation functions are used to simulate the data at the small and medium angles, and a perturbation of these functions with two additional parameters allows the fit of the upward and downward curve portions of the data at the large angles. Good agreement is found with previous results. The present approach is the same as the classical dispersion equation in treating the index of refraction of optical materials.