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It has been considered formerly that the reason why ZnS coating is not able to stand the environmental corrosion is the cross section structure of its column,1 the gaps among the columns and the capillaries formed by the gaps. The gaps among the columns of ZnS coating deposited on the substrate at low temperature are rather big, the packing density is low, so the coating can not have better mechanical pro— perties.2 To obtain ZnS coating with high strength it is necessary to enhance the temperature of the substrate during deposition. But the problem is that the higher the temperature is, the lower the deposition - speed will be. 200°C is nearly the temperature limitation of the substrate at which the deposition can be done. This fact also hinders us to enhance the strength of the coating. Addi tionally, after the temperature of the substrate has been enhanced, the grains of the coating become bigger, and the coating surface becomes more rough. An anti reflecting coating with good optical property must be a film formed by very fine grains. When it serves as a laser coating it must have a uniform and isotropic heat conductivity, therefore the structure formed by fine grians is necessary to enhance laser damage threshold. So it gives rise to inconsistency between the mechanical property and the optical property of the coating. This paper describes a new type of ZnS coating which has been deposited at low temperature, so it possesses fine grains and therefore its optical property is excellent. After annealing, the texture of the coating has been turned from pref érential orientation of (111) surface into that of (iiO),' at the same time, the coating possesses high strength and chemical stability, especially, its laser damage threshold is 1.9 times as high as that of the common one. This coating can be made either on monocrystal line substrate or glass substrate, with a coating area < 200 mm. In the last two years the authors have offered many ZnS coating with high optical properties and high strength as outside surface coating for the laser and thermal imaging systems
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