UV-laser-induced contamination: a parametric study of deposit morphology

"Laser-induced contamination" is a major difficulty for high power photonics instruments in vacuum and in sealed environments. Material outgassing causes molecular contamination on the optical components where the laser irradiation causes photo-fixation and/or polymerization leading to carbonaceous deposits at the location of the laser beam. We studied the morphology of these deposits as function of several parameters of physical and chemical nature. The influence of these parameters on the crater rim height of the "donut"-type deposits are presented and lateral growth of the deposits beyond the laser beam size is observed. The observation of lateral growth beyond the laser beam size indicates an influence of thermal energy input to the deposition process. We hypothesize that this thermal energy is provided by heat conduction from the center of the crater.