Molecular contamination testing with continuous-wave laser radiation at 1064 nm: de-risking activity for the LISA space mission

We investigate effects of laser-induced contamination (LIC) with contaminant materials and laser parameters relevant for the LISA space mission. To accelerate outgassing and a possible deposit formation, the contaminant materials have been heated to a temperature of up to 100 °C (nominal operating temperature of 20° C), and LIC tests were performed with a laser power density of up to 300 W/cm2 (to be compared with expected 125 W/cm2). Neither in-situ measurements (laser transmission, polarization and wavefront), nor a careful microscopic inspection of the optical surfaces after the LIC tests showed indications of a laser-induced deposit formation. Condensation on optical surfaces could be observed. This is cautiously encouraging for LISA and indicates that the LIC concern may be reduced compared to what observed at shorter wavelength or with pulsed laser radiation