Anomalous Refraction Maxima in the Bidirectional Transmittances of Roughened Dielectric Surfaces
Final rept. Jul 1970-Sep 1971
ARNOLD ENGINEERING DEVELOPMENT CENTER ARNOLD AFB TN
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Bidirectional distribution measurements were made of the plane- polarized radiant flux transmitted through roughened glass samples having various surface roughnesses. These monochromatic measurements were made in the plane of incidence as a function of the irradiance zenith angle. For an irradiance angle of 0 deg, it is found that as the surface roughness-to- wavelength ratio increases the relative binormal transmittance of the glass decreases and the bidirectional transmission distributions become more diffusing but do not approach a Lambertian distribution. For off-normal irradiance angles and surface roughness-to-wavelength ratios significantly greater than unity, the maxima in the bidirectional transmission distributions of the roughened glass samples occur at zenith transmission angles smaller than those prescribed by the macroscopic application of Snells refraction equation to a transmitting surface system. These transmission extrema have been termed anomalous refraction maxima and their angular displacement from the Snell direction is found to increase with increasing surface roughness and zenith incidence angle.