Cryogenic thermal noise testbed for low-temperature interferometry
Proposals for future gravitational wave detectors explore the use of cryogenically cooled optics to reduce thermal noise in the detector readout. This noise is predominantly caused by the thermal energy in the primary mirrors and suspensions, and the accompanying statistical temperature fluctuations.
Cooling the critical interferometer components to certain "sweet spot" temperatures can mitigate thermal noise but involves operating cryogenic equipment close to the vacuum chambers, which fundamentally conflicts with efforts to isolate the mirrors from seismic and acoustic disturbances. The necessary compromise limits the achievable cooling power, which competes with the residual absorption of the high optical powers that circulate in gravitational wave interferometers. The mechanical and thermal characteristics of the coating, substrate, and suspension materials need to be thoroughly explored in the low-temperature regime to confirm their superior thermal noise performance, which relies on the mutual cancellation of different thermal effects, the optimization of coating structures, and the suspension geometry.
At the ANU Centre for Gravitational Physics we are constructing one of the first testbeds for such investigations of optical, thermal, and mechanical properties of candidate coatings and suspension designs.