Structural materials with extremely low coecient of thermal expansion (CTE) are crucial to enable ultimate
accuracy in terrestrial as well as in space-based optical metrology due to minimized temperature dependency.
Typical materials, in particular in the context of space-based instrumentation are carbon-ber reinforced plastics
(CFRP), C/SiC, and glass ceramics, e.g. Zerodur, ULE or Clearceram. To determine the CTE of various samples
with high accuracy we utilize a highly symmetric heterodyne interferometer with a noise level below 2 pm√Hz at frequencies above 0.1 Hz. A sample tube made out of the material under investigation is vertically mounted in
an ultra-stable support made of Zerodur. Measurement and reference mirrors of the interferometer are supported
inside the tube using thermally compensated mounts made of Invar36. For determination of the CTE, a sinusoidal
temperature variation is radiatively applied to the tube. One of the essential systematic limitations is a tilt of
the entire tube as a result of temperature variation. This tilt can simultaneously be measured by the DWS
technique and can be used to correct the measurement. Using a Zerodur tube as a reference, it is shown that
this eect can be reduced in post processing to achieve a minimum CTE measurement sensitivity <10 ppb/K.