Lasing in Open Microcavities with Active Regions as a Linear Electromagnetic Eigenproblem

A review of the recently proposed approach to the analysis of lasing as a linear eigenproblem for the Maxwell equations with exact boundary and radiation conditions is presented. It is based on the assumption that the cavity contains an active region characterised by the "active" imaginary part of refractive index. This enables one to quantify the thresholds of lasing, for each of the cavity modes, and to use the tailoring of the shape of the active region as an instrument for lowering the thresholds.