ORIGINS OF FUNDAMENTAL LIMITS FOR REFLECTION LOSSES AT MULTILAYER DIELECTRIC MIRRORS

Fundamental limits on reflection losses are set by internal material l osses associated with the Urbach tail near a band gap and by thermodyn amic density fluctuations in fabrication. In materials such as SiO2 an d TiO2, these limits are of the order of parts in 10(9). The current q uality of supercavity mirrors, in contrast to that of optical fibers, is still far from these limits because of purely technological limitat ions in surface preparation and in the reduction of impurity levels. O vercoming these would greatly benefit, for example, Fabry-Perot interf erometers, ring lasers, and gravitational wave detectors.