28 September 1994 Diamond coatings for large-area IR windows
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Abstract
The use of diamond to coat ZnS discs of 1' diameter has been reported previously. In order to make this process commercially useful, diameters of greater than 4' are required. The process of scaling up requires issues such as uniformity, morphology, and IR quality of the coating to be addressed. The main advantages of a diamond coated IR window compared with a bulk diamond window are that the relatively thin coating would have good transparency in the mid IR region (3 - 5 micrometers ) and that the cost may be considerably lower. The latter would certainly be the case if the coating did not require post growth polishing. It has been estimated that in the next generation 8 - 12' diameter diamond windows, the required polishing may well be the most expensive part of the production process. This paper describes work using an 8' diamond coating system, and looks at issues such as IR transparency, surface morphology (surface scatter) and thickness uniformity, and how this process can be applied to coating large area IR windows such as ZnS and Ge. Evidence is presented that coatings of 10 - 20 micrometers thickness can be applied having good IR transparency with a sufficiently smooth as-grown surface such that scattering in the IR is negligible. This is compared with free-standing disks of mm thickness where surface scatter on the as grown face makes polishing essential.
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Crofton J. Brierley, Crofton J. Brierley, Mark C. Costello, Mark C. Costello, Martin D. Hudson, Martin D. Hudson, T. J. Bettles, T. J. Bettles, } "Diamond coatings for large-area IR windows", Proc. SPIE 2286, Window and Dome Technologies and Materials IV, (28 September 1994); doi: 10.1117/12.187352; https://doi.org/10.1117/12.187352
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