During the annual NIST calibration testing done at the LHMEL facility in FY06 on its high energy Carbon-Dioxide lasers, the LHMEL II device suffered severe damage to the internal surface of its ZnSe output
coupler optics. The damage occurred during a high power, short duration run and it was believed to have
been the result of a significant amount of surface contaminants interacting with the LHMEL cavity beam.
Initial theories as to the source of the contamination led to the inspection of the vacuum grease that seals
the piping that supplies the source gases to the laser cavity. Other contamination sources were considered,
and analysis was conducted in an effort to identify the material found at the damage sites on the optic, but
the tests were mainly inconclusive. Some procedure changes were initiated to identify possible
contamination before high energy laser operation in an attempt to mitigate and possibly prevent the
continued occurrence of damage to the output coupler window. This paper is to illustrate the type and
extent of the damage encountered, highlight some of the theories as to the contamination source, and serve
as a notice as to the severity and consequences of damage that is possible even due to small amounts of
foreign material in a high energy laser environment.