Optical Cryogenic Silicon Resonators

The tremendous progress with optical atomic clocks asks for super-stable lasers to interrogate the best clock transitions with only a few mHz line width. Previously, we developed a cryogenic silicon Fabry-Perot resonator that demonstrated short-term instability below 1 × 10 -16 . We have set up two independent updated systems with the goal of reaching a thermal-noise limited fractional frequency instability of about 5 × 10 -17 . We report on the current progress.