Optical scattering measurement of highly reflective coatings with the cavity ring-down technique

Cavity ringdown (CRD) is employed for the first time, to the best of our knowledge, to precisely measure the optical scattering of highly reflective (HR) optics with measurement sensitivity greatly enhanced via power trapping inside the ringdown cavity. The scattering measurement accuracy is significantly improved by calibrating the photo-detector for the scattering measurement with the low transmittance of the cavity mirror or test HR mirror, which is also accurately measured by CRD. The influence of environmental stray light (such as the probe light scattered by optics and mechanical parts outside the ringdown cavity) and other background noises on the scattering measurement is greatly eliminated by the temporal behavior of the scattering CRD signal. A scattering measurement sensitivity of 4.0 × 10^-13 is experimentally achieved with a laser with output power of 12 mW.