Space applications demand light weight materials with excellent dimensional stability for telescopes, optical benches, optical resonators, etc. Glass-ceramics and composite materials can be tuned to reach very low coefficient of thermal expansion (CTE) at different temperatures. In order to determine such CTEs, very accurate setups are needed. Here we present a dilatometer that is able to measure the CTE of a large variety of materials in the temperature range of 140 K to 250 K. The dilatometer is based on a heterodyne interferometer with nanometer noise levels to measure the expansion of a sample when applying small amplitude controlled temperature signals. In this article, the CTE of a carbon fiber reinforced polymer sample has been determined with an accuracy in the 10 K range.

Marginal changes in geometrical dimensions due to temperature changes affect the performance of optical instruments. Highly dimensionally stable materials can minimize these effects since they offer low coefficients of thermal expansion (CTE). Our dilatometer, based on heterodyne interferometry, is able to determine the CTE in 10 À8 K À1 range. Here, we present the improved interferometer performance using angular measurements via differential wavefront sensing to correct for tilt-to-length coupling. The setup was tested by measuring the CTE of a single-crystal silicon at 285 K. Results are in good agreement with the reported values and show a bias of less than 1%.