Observation of optomechanical coupling in crystalline whispering gallery mode resonators

The coupling of optical and mechanical degrees of freedom gives rise to a number of long-anticipated phenomena, such as cooling or amplification of mechanical motion. Particularly promising candidates for the emerging field of cavity optomechanics are microresonators such as silica microtoroids [1]. However, these structures suffer from strong mechanical dissipation at cryogenic temperatures, caused by two-level fluctuators in the amorphous material. It is therefore of interest to use a crystalline material such as quartz or CaF
2
, which supports mechanical Q factors ≫10
⁸
at low temperatures [2]. While crystalline whispering gallery mode resonators, as pioneered by Maleki and co-workers have attained record Q factors exceeding 1011 in the optical domain [3], their optomechanical properties have so far neither been observed nor studied.