TEMPERATURE-COMPENSATED CRYOGENIC FABRY-PEROT CAVITY

We show that temperature compensation based on differential thermal ex pansion between sapphire and fused silica can be used to create a Fabr y-Perot cavity viith an exceptionally low coefficient of thermal expan sion at low temperatures. We describe the design of such a cavity that utilizes shaped fused silica mirrors and a sapphire spacer. The geome try of the fused silica mirror was designed using a finite element mod el to have a small platform, giving a frequency temperature turning po int of 16.6 K. The measured turning point was 16.2 K and the curvature was 6 x 10(-10) K-2, both of which were consistent with the model. (C ) 1997 Optical Society of America.