Аннотация:We present a detailed analysis of the effect of volumetric and surface inhomogeneities as a source of quality-factor limitation and intracavity resonant backscattering in optical microsphere cavities of fused silica. Intrinsic scattering in microspheres is shown to be significantly inhibited as compared to standard Rayleigh scattering in the bulk material. This reassessment of fundamental losses indicates that Q-factors substantially exceeding the previously expected limit of similar to 10(11) can be obtained in microspheres, as soon as surface hydration is prevented. The intracavity backscattering is analyzed as a source of whispering-gallery mode splitting and resonant optical feedback in presence of a mode-matched travelling-wave coupler.