A second generation of low thermal noise cryogenic silicon resonators

Abstract

We have set up an improved vertically mounted silicon cavity operating at the zero-crossing temperature of the coefficient of thermal expansion (CTE) near 123 K with estimated thermal noise limited instability of 4 x 10-17 in the modified Allan deviation. Owing to the anisotropic elasticity of single-crystal silicon, the vertical acceleration sensitivity was minimized in situ by axially rotating the resonator with respect to the mounting frame. The control of the resonator temperature is greatly improved by using a combination of two thermal shields, monitoring with several temperature sensors, and employing low-thermal conductivity materials. The instability of the resonator stabilized laser was characterized by comparing with another low-noise system based on a 48 cm long room temperature cavity of PTB's strontium lattice clock, resulting in a modified Allan deviation of 7 x 10-17 at 100 s.