Low-Absorption Laser Windows
Semiannual report Number 1, for Period Ending 31 Dec 1975
NAVAL RESEARCH LAB WASHINGTON DC
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This semiannual report summarizes work by NRL under ARPA Order 3066. Improvements have continued in methods for preparation, surface finishing, and characterization of low-loss laser-window materials. Calorimetric absorption studies included measurements of eight alkali and alkaline earth halides at 1.06 micrometers and of calcium fluoride, zinc selenide, and several alkali halides at 2.7, 3.8, and 10.6 micrometers. Adequate surface preparation virtually eliminates detectable surface absorption. Carbon tetrachloride is the most effective reactive halide for purification of potassium bromide, which was shown by bulk absorption coefficients for KBr as low as 0.000003 per centimeter at 1. 06 micrometers and 0.000014 per centimeter at 10.6 micrometers but nevertheless 0.0001 to 0.0002 per centimeter at 2.7 and 3.8 micrometers and by the absence of metaborate ions in the crystals. A polishing method analogous to that for KCl was found effective for KBr, resulting in pit-free surfaces stable to room air for over a week, especially for surfaces remote from cleavage planes. Appended to this report is an abstract of a Navy-sponsored paper which compares crack propagation in alkali halides with that in alkaline earth fluorides. Future studies for which some crystals have been prepared will involve purification of strontium fluoride, additive strengthening of potassium chloride and potassium bromide, and testing of an evacuated calorimeter.
- Lasers and Masers
- Infrared Detection and Detectors