Combined molecular and metallic particulate laser-induced contamination testing: de-risking activity for the LISA space mission

To mitigate risks due to laser-induced contamination (LIC) for the LISA space mission, we have carried out an extensive LIC test campaign, including a series of short duration tests with different test parameters, as well as a long-duration test. Those previous experimental results as well as theoretical considerations indicate that LIC might be less of a concern for the LISA mission. A remaining concern is whether LIC could occur in the presence of metallic particles on optical surfaces and whether a higher pressure does have an impact. Our ongoing research thus aims at testing for a possible deposit formation in a combined LIC and metallic particulate contamination test. Therefore, a HR optics is contaminated with metallic (aluminum) particles, mounted in the sample holder and tested within a similar test setup used for previous tests. The test is performed at a pressure similar to the actual expected pressure of 10^-5 mbar at the optical bench during the mission (previous tests at 10^-8 mbar). These tests do not indicate that LIC is a concern and metallic particulate contaminants seem not to accelerate or trigger LIC in this laser regime.