Development of a Sub-Kelvin Silicon Cavity

We report a pathfinder to address the current limitations of ultrastable lasers based on optical Fabry-Perot cavities, aiming to set the ground for the next generation targeting frequency instabilities below 1×10
^-17
. This pathfinder proposes to frequency stabilize a 1.5 µm laser to a silicon Fabry-Perot cavity with crystalline Al0.92Ga0.08As/GaAs mirror coatings at sub-Kelvin temperature. This temperature is reached by using cryogenic dilution refrigerator.