The usage of satellite constellations operating several identical or very similar satellites is more and more common. For best cost efficiency these satellites should be produced in parallel or at least one right after the other, even if their launch dates may be separated by several months or even years. However, after assembly, integration, testing and storage, even in clean room conditions, molecular contamination is observed on the surfaces. This molecular contamination originates from partial condensation of the outgassing species of organic materials. Particularly for optical components, the layer of molecular contaminants may cause important performance loss during operation of the satellite in vacuum. Thus cleaning the critical elements from molecular contamination is necessary before launch.

However, cleaning of these elements may not be possible because optical elements may be difficult to access after final system integration. This is the reason why in this study we explore the feasibility of non-contact cleaning by laser irradiation in the presence of oxygen and humidity.

According to literature UV wavelengths give the best cleaning results and we use the forth harmonic of a q-switched Nd:YAG laser at 266 nm. On components that absorb 266 nm, the main difficulty is shaping the laser beam to a flat top beam profile. On one hand, to avoid laser induced “contamination” (LIC) the contamination layer should not be irradiated with too small fluences. On the other hand, to avoid laser induced damage, the substrate should not be irradiated with too high fluences. Thus the flat top properties of the beam shape are very important. We used a refractive and a diffractive beam homogenizer and obtained good cleaning results with both of them. The cleaning efficiency has been evaluated by optical microscopy, optical profilometry and by FTIR transmission measurements on various substrates.