A Cryogenic Testbed for High-Q Thin Films and Optical Coatings

A limiting source of noise for optomechanical experiments, including next-generation gravitational wave detectors, is coupling to the thermal bath of the mechanical system. We present a recently developed cryogenic testbed for measuring the internal friction of thin disk resonators with rapid sample turnover. The apparatus makes use of an amplitude-locked loop to continuously measure the quality factor and eigenfrequencies of several resonances of the system, permitting precise, non-contact temperature control. The testbed has been applied to the development of amorphous silicon coatings on silicon substrates for use in next-generation gravitational wave interferometers, and has application for other thin film development.