New frontiers in electromagnetics: Modal analysis of lasers as open resonators with active regions

Presented is the linear electromagnetic theory of lasers as open dielectric resonators with active regions. This is called the Lasing Eigenvalue Problem (LEP); it is specifically adapted to the extraction of the lasing mode material-gain thresholds in addition to the frequencies. The Poynting Theorem applied to the LEP solutions yields a useful expression linking the threshold gain with mode´s Q-factor and overlap coefficient. The approach is illustrated with modes of a two-disk laser where only one disk is active, and a kite-shape fully active laser.