Laser-Induced Molecular Contamination on Space Optics: Comparison of Test Results with Infrared Continuous-Wave and Nanosecond Pulsed Lasers

Laser-induced molecular contamination (LIMC) describes the formation of solid deposits due to the interaction of laser radiation with outgassing molecules on optical surfaces. The understanding and mitigation of LIMC is particularly relevant for space optics, because optics in space often require long-term usage (several years), operate under vacuum and cannot be cleaned nor replaced. In addition, space missions involving lasers require several years (or even decades) of preparation. We report on recent results of the LIMC test campaign with a continuous-wave, infrared laser that was carried out in the framework of the LISA mission. These results are compared and put in context to previous studies using nanosecond pulsed laser, particularly in the frame of the Aeolus and the EarthCARE space missions. LIMC is a complex field of laser-driven surface chemistry and has been studied primarily to mitigate risks of specific space missions, rather than with an emphasis on fundamental investigations. Nonetheless, we use the comparison of experimental results to extract specific insights into the mechanism of deposit formation such as the relevance of multiphoton absorption. Given the many applications for lasers in space, we point out how future research could contribute to an even better understanding of LIMC on the molecular level and to the advancement of strategies for their mitigation.