Many analyses are found to be simpler in direction cosine coordinates. The analyses occasionally concern data obtained at angles far from specular. In order to avoid design error, the magnitude of the difference between transformed value and measured value must be known. Three Si discs (two uncoated and one coated with Al) were tested. All tests began with normal incidence. First, the sample was fixed and the detector was moved in 5.0 degree intervals about a vertical axis to measure reflective scatter. In the second test, the sample was simultaneously rotated about the same axis but in the opposite direction in order to yield 0.1 intervals in direction cosine coordinates. The data from the first test were transformed into direction cosine coordinates and compared. The transformed data began diverging significantly from the direct data at about 15.0 degrees. This report investigates the region of divergence.
Scatter measurements were performed on one sample each of ZnSe and ZnS (sometimes called 'cleartrans') in 5.0 degree intervals from 5.0 degrees to 180 degrees (an additional point, 3.7 degrees from specular was also obtained). Two detectors were available: A battery powered Si detector, used in the voltage mode and chosen to match potential IR sources and a photomultiplier tube (PMT, used in the current mode), chosen to match a visible source such as a Xe arc lamp. Two sources were available. The first was an HeNe laser operating at 6328 Angstroms with a nominal power of 15 mW. The second was a Xe arc lamp with an input of 1000 watts. The lamp was used, alone, as a broadband source or it was used with an interference filter having peak transmission of 5000 Angstroms and bandwidth of 100 Angstroms. The resulting matrix of 12 tests characterizes the relative scatter from these two materials over a significant part of the visible spectrum and demonstrates the potential difficulties in comparing tests with differently convolving source-detection systems.
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