Studies at Litton Laser Systems Division (LLSD) and other laser vendors have found that in a hermetically sealed laser, trace levels of gas phase contaminants can lead to photo-induced optical damage. This damage has been shown to occur at power densities as low as 20 MW/cm2 on uncoated quartz substrates. Since contamination-induced optical damage can be a significant factor in reducing laser reliability and lifetime, it is important to understand the mechanisms by which it occurs. In this paper we will describe investigations performed at LLSD on the mechanisms of contamination-induced optical damage. The starting point for these studies is a simple test developed at LLSD to evaluate the potential of materials in sealed optical compartments to cause contamination-induced damage. A systematic study of the morphology, composition, chemical species dependence, and initiation time of contamination-induced optical damage allow a number of qualitative conclusions concerning the damage mechanism to be deduced.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.