The Effect of Moisture and Temperature on Optical Coatings Used in Eye-safer Lasers

Report No. ARL-TN-0408
Authors: Jeffrey O. White, Aaron Z. Chan, and Carl E. Mungan
Date/Pages: September 2010; 18 pages
Abstract: Erbium (Er):yttrium aluminum garnet (YAG) lasers are currently under development at the U.S. Army Research Laboratory (ARL) as eye-safer alternatives to neodymium (Nd):YAG for countering rockets, artillery, and mortar (CRAM). Anomalous increases in laser output have been observed during the 30-60 min period after turn-on. A hypothesis was that one or more of the three optical coatings (anti-reflection, dichroic, and partially reflecting) in the laser cavity were absorbing or desorbing moisture. On the basis of the baking-out measurements described here, we attribute the increase in laser power to moisture being driven out of the dichroic coating, increasing its reflectivity at the laser wavelength. We have also measured the effect of operating temperature on a dichroic coating that has already been baked-out.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2010