Very high Q frequency-locked Fabry–Perot cavity

Abstract
We report measurements on a 1.75 m long Fabry–Perot cavity locked to a Nd:YAGtunable laser using the Pound–Drever technique. The cavity decay time was measured to be about 291 μs corresponding to a quality factor Q of about 5×1011, the highest value ever reported for an optical resonantcavity.