In our structural dimensional metrology laboratory, we implemented a setup to determine coefficients of thermal expansions (CTE) of ultra-stable materials at temperatures from 300 K down to 100 K. Such low CTE materials are important for dimensionally stable structures in space and terrestrial applications, e. g. to enable precise measurements. This CTE characterization is done in the 10 ppb/K (10·10-9 K-1) range by applying small temperature variation around dedicated absolute temperatures. In order to accommodate arbitrary sample materials, we bounce light off mirrors attached to the sample by custom mounts. The light and therefore the thermal-induced length variations is then analyzed by an interferometer with sub-nanometer sensitivity. Here, we present a more detailed investigation of a process during sample measurements using differential wavefront sensing (DWS)
