In-situ laser-induced contamination monitoring using long-distance microscopy

Kurzfassung

Operating high power space-based laser systems in the visible and UV range is problematic due to laser-induced contamination (LIC). In this paper LIC growth on high-reflective (HR) coated optics is investigated for UV irradiation of 355 nm with naphthalene as contamination material in the range of 10-5 mbar. The investigated HR optics were coated by different processes: electron beam deposition (EBD), magnetron sputtering (MS) or ion beam sputtering (IBS). In-situ observation of contamination induced damage was performed using a long distance microscope. Additionally the onset and evolution of deposit formation and contamination induced damage of optical samples was observed by in-situ laser-induced fluorescence and reflection monitoring. Ex-situ characterization of deposits and damage morphology was performed by differential interference contrast and fluorescence microscopy. It was found that contamination induced a drastic reduction of laser damage threshold compared to values obtained without contamination. Contamination deposit and damage formation was strongest on IBS followed by MS and smallest on EBD.