Laser-induced contamination on high-reflective optics

Abstract

Operating high power space-based laser systems in the visible and UV range is problematic due to laser-induced contamination. Organic materials are outgassing in vacuum and deposit on irradiated optical components. To provide reliable space-based laser systems the optical components quality plays a major role. In this thesis laser-induced contamination growth on high-reflective coated optics is investigated for UV irradiation of 355nm with naphthalene as contamination material. Four different kinds of optics were investigated: three high-reflective coated optics fabricated by Electron Beam Deposition, Magnetron Sputtering and Ion Beam Sputtering technique and one anti-reflective coated optic fabricated by Electron Beam Deposition technique. The contamination test procedure was designed to perform laser-induced contamination tests on 45° high-reflective coated optics. For the first time 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 microscopy and fluorescence microscopy. It was found that at a partial pressure of contamination material in the range of 10E-5mbar induced a drastic reduction of laser damage threshold compared to values obtained without contamination.