TEMPERATURE COMPENSATION FOR CRYOGENIC CAVITY STABILIZED LASERS

We describe a cryogenic Fabry-Perot cavity in which a frequency-temper ature turning point at 43 K is created by differential thermal contrac tion between the mirrors and the spacer. The cavity uses a sapphire sp acer and fused silica mirrors. The expansion coefficient of the spacer is balanced by a negative term arising from the outward flexing of th e mirrors caused by differential radial expansion of the mirror substr ate and spacer. A simple model indicates that is possible to construct cavities with shallow turning points of frequency-temperature at temp eratures between 10 and 65 K.