RESEARCH ON OPTICS OF SELECTIVE SURFACES.
Final rept. for 1 Sep 599-31 May 63,
HEBREW UNIV JERUSALEM (ISRAEL)
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Selective surfaces for solar energy absorbers comprise a metal base, of low intrinsic thermal emissivity modified - usually by the addition of surface coatings to obtain a high absorptivity to solar radiationoion with as little increase as possible to the emissivity. This combination constitutes a reflection filter. The programme concerned itself primarily with nickel-black coatings produced by electro-deposition. It was shown that the chemical and optical properties of these coatings varies with thickness and with the conditions in the placing bath. New optical and mathematical techniques were developed to determine the optical constants of thin absorbing layers which are not necessarily isotropic in depth and how to manipulate them to produce filters with desired characteristics. Early selective surfaces of this kind used a pair of different nickel-black layers on a metal base and passable filter properties were obtained. Development of the theory of these surfaces suggested the addition of an intermediate layer metallic to produce a three-layer system with a very broad interference region in the solar spectrum. Some work was started on other blacks such as chromium-black. Author