The reflectance and optical constants of films of zinc sulfide vacuum deposited onto glass have been measured for the wavelength region extending from 2200 to 584 A. The effects of different deposition conditions and aging in normal and dry air were studied. In the wavelength range from 2200 to 1100 A the reflectance is relatively high (≈33%) and uniform. Beyond 1100 A it decreases and at 584 A is only 3.8%. The refractive index, n, decreases rapidly from a value of 3.13 at 2200 A to a minimum of 0.64 at 735 A. The absorption coefficient, k, has a maximum value of 1.75 at 1800 A and decreases with decreasing wavelength to a value of 0.23 at 584 A. In contrast to many other materials the variation of deposition conditions has very little effect on the reflectance of zinc sulfide. The films also show almost no aging in normal or dry air. Under the best conditions these films are durable enough to stand washing with cotton and detergent many times without damage.
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