Quantum theory of cavity quasimodes

Abstract

Mode decompositions inside imperfect cavities have been common since the early days of laser theory. The resulting quasi-modes form a discrete set with diffraction and transmission losses modelled by phenomenological processes. We employ a Fano-type analysis to compare the quasimode and more rigorous full normal-mode decompositions. Our analysis provides a justification for the quantisation of cavity quasimodes in the good cavity limit.