16 October 2002 Reflectivity of the Al-Cr stray-light-absorptive coating
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Abstract
Results of measurements of the total hemisphere reflectance (THR), emissivity ε and solar radiation absorption factor αs of the Al-Cr stray-light-absorptive coating are reported. This coating was designed to reduce the stray sunlight background in aerospace instruments. Generally, this problem arises when a density of instruments installed on the satellite is high and it is difficult to avoid getting to instrument the light reflected by neighboring devices. The THR, ε, and αs measurement results are presented for 10 wavelengths within a range from 400 to 927 nm, and also at 121.6 nm, the most intensive line of the solar UV spectrum, which is able to create considerable contribution to the detector noise in space devices. The goal of present experiments was to test an idea that by providing the electron scattering in the coating skin layer, it is possible to reduce the THR. To have the samples with increased electron scattering intensity, the samples of the Al-Cr coating were manufactured. As in teh Al-Cr alloy the d-band of chromium electrons is located in the vicinity of the Fermi energy of Al, in this alloy a considerable electron scattering takes place. Therefore, within the skin layer of such coating, the electrons excited by photons transfer their energies and momenta to the lattice and other electrons instead of releasing the secondary photons. Hence, the reflectivity of the Al-Cr coating might be reduced. The prepared samples and performed experiments confirmed this assumption. According to the measurement results, the chromium appears to be an acceptable additional admixture to provide a further reflectivity reduction in the previously sutdied promising Al-N coating.
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Vladimir P. Anisimov, Irina A. Anisimova, Kamil A. Moldosanov, Alexander M. Skrynnikov, Victor A. Kashirin, "Reflectivity of the Al-Cr stray-light-absorptive coating", Proc. SPIE 4767, Current Developments in Lens Design and Optical Engineering III, (16 October 2002); doi: 10.1117/12.451227; https://doi.org/10.1117/12.451227
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