1 September 1991 Thick, fine-grained beryllium optical coatings
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Fine grained, sputter-deposited Be coatings with thicknesses up to 290 microns have been laid down on six coupons of various substrate materials including S-200 grade beryllium, SiC and Ti6Al4V alloy. Each coated substrate was subsequently polished to a very low surface roughness (less than 5 A rms) finish by one of two different polishing techniques. Bidirectional reflectance distribution function (BRDF) measurements were taken at 632.8 nm and at 10.6 microns. BRDF values at 10.6 microns were measured as low as 9 x 10 exp -7/sr at 10-deg off-specular. Calculated power spectrum density curves showed remarkably little or no anomalous scatter except for one coating laid down with no substrate bias and an uncooled substrate. The measured reflectances of the polished Be coatings at 10.6 microns is about 5 percent below that for the gold reference surface (i.e., about 94 percent of absolute reflectance).
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Brian W. Murray, Eric Ulph, Peter N. Richard, "Thick, fine-grained beryllium optical coatings", Proc. SPIE 1485, Reflective and Refractive Optical Materials for Earth and Space Applications, (1 September 1991); doi: 10.1117/12.46528; https://doi.org/10.1117/12.46528

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