Laser-induced contamination and its impact on laser damage threshold

In this paper some basic investigations about laser-induced contamination are reported. As contamination materials pure aromatic hydrocarbons (naphthalene and anthracene) were used. A particular focus of the tests was to investigate the impact of laser-induced contamination on damage threshold. Onset and evolution of deposit formation and damage were observed in-situ by laser-induced fluorescence and transmission monitoring. As optical samples uncoated fused silica substrates and AR and HR coated optics with different coating morphology, depending on coating process (e-beam, magnetron sputtering) were investigated. Ex-situ characterization of deposits and damage morphology was performed by differential interference contrast, fluorescence, and atomic force microscopy. The tests were run with pulsed UV light at 355 nm. Partial pressure of contamination material in the range of 10(-4) mbar induced a drastic reduction of laser damage threshold compared to values obtained without contamination.