Dilatometer setup for low coefficient of thermal expansion materials measurements in the 140 K-250 K temperature range

Abstract

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.

Laser-dilatometer calibration using a single-crystal silicon sample

“…It is clear that TTL has an impact on the length measurement, which can be mitigated by measuring it and subtracting it in post-processing. In our previous setup [13] such functionality was not yet enabled due to problems with the optical read-out and only an estimation of the coupling was possible, which supported the behavior shown in Figure 2(D). The optical read-out has been upgraded to allow DWS measurements.…”

“…A short description of the setup with the latest upgrades is given in the following. A detailed description of our setup is given in our previous publication [13] . Our dilatometer is split into several subsystems.…”

“…For instance, in this simulation DL increases from the ideal 260 nm to 279 nm, where the 19 nm difference is due to the tilt of the sample, which is measured by both b QPD . Previous experiments [13] have shown that the most likely scenario in our setup is the one described in (D), which would allow us to correct it by taking into account the DWS read-out. Consequently, in the following, we assume scenario (D), i.e., common tilt of sample and mirrors (M1 and M2).…”

“…To validate these designs and manufacturing processes, the materials have to be characterized, which can be done with a dilatometer to obtain the CTE. We operate a laser-interferometric dilatometer, which allows CTE characterization in a temperature range from 140 K to 250 K with uncertainty levels of 10 À8 K À1 [13] . Unique to this dilatometer is its interferometric read-out, which gives information about length change and sample tilting.…”

“…In this manuscript, we present the latest results of our dilatometer, which allows us to characterize CTEs at the 10 À8 K À1 level. Our previous setup [13] was found to be limited by tilt-to-length coupling, i.e. a tilt of the sample under test introduced an error in the length measurement that could not be corrected since the setup was unable to measure angles.…”