2 SIMPLE EXPRESSIONS FOR THE SPONTANEOUS EMISSION FACTOR-BETA

In the literature two different simplified expressions exist for the s pontaneous emission factor beta, being the fraction of spontaneous emi ssion radiated into a specific optical mode. These expressions are val id in two mutually exclusive regimes. By treating the coupling between one discrete cavity mode and the outside optical continuum quasi one dimensionally in the spirit of Fano [Phys. Rev. 124, 1866 (1961)], we extend the validity range of both expressions and show that they lead to essentially the same result. The relevance and limitation of this r esult are discussed.