Removal of laser-induced contamination on ALADIN laser optics by UV/ozone cleaning

Abstract

The ESA satellite Aeolus was successfully launched into space in August 2018 and measures global wind profiles using the Atmospheric Laser Doppler Instrument (ALADIN). ALADIN features a high-power UV laser source emitting nanosecond pulses at a wavelength of 355 nm. A crucial step in the development of ALADIN was the mitigation of laser-induced contamination (LIC). In this work we assess the opportunity of removing LIC deposits using UV/ozone cleaning with a mercury lamp. We find that UV/ozone cleaning is a very effective tool for removing laser-induced molecular contamination induced by the volatile components of a material mix representative of the ALADIN laser. Furthermore, we show that optical surfaces on which a contamination is removed via UV/ozone cleaning behave similar to pristine optical surfaces with respect to their susceptibility to subsequent LIC as well as laser-induced damage. These results demonstrate that UV/ozone cleaning is a useful and safe way of cleaning optical surfaces after ground-based thermal vacuum/lifetime testing.