Abstract
We describe a cryogenic Fabry-Perot cavity in which a frequency-temperature turning point at 43 K is created by differential thermal contraction between the mirrors and the spacer. The cavity uses a sapphire spacer and fused silica mirrors. The expansion coefficient of the spacer is balanced by a negative term arising from the outward flexing of the mirrors caused by differential radial expansion of the mirror substrate and spacer. A simple model indicates that is possible to construct cavities with shallow turning points of frequency-temperature at temperatures between 10 and 65 K.
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