In-situ characterization of high-power laser-induced thermal deformation of MEMS micromirrors in vacuum

This work employed an integrated approach combining numerical simulations and experimental measurements. The systematic investigation focused on the thermal deformation characteristics of large optical aperture MEMS fast steering mirrors (FSM) under high-power laser irradiation in vacuum. This work established a vacuum-compatible surface figure testing system and proposed an absolute surface figure measurement methodology. Three experimental sample groups with distinct initial surface figures were investigated for their deformation characteristics under 0.5-5 W laser irradiation. Differences in surface figure deformation were observed among the three sample types. The suitable power ranges differ among the three samples. Under 5 W laser irradiation, the maximum mirror surface temperature reached approximately 80°C. After irradiation, optical and surface properties remained across all tested power levels, with reflectance variations limited to < 0.3% and surface roughness changes constrained to < 2 nm. The mirror surface figure exhibited recovery to the initial level by natural convection. The reversible nature of laser-induced thermal deformation originates from the mismatch in coefficients of thermal expansion (CTE) between constituent materials.