Characteristics of parasitic eigenmodes in high-average-power disk lasers

Abstract

The parasitic oscillations in a disk gain medium are refined by a rigorous electrodynamics study. The boundary conditions of an electromagnetic field decide not only the spatial distribution of the field (transverse eigenmodes) but also the spectrum of the field (longitudinal eigenmodes) due to the higher geometric symmetry of the disk. The novel dispersion relations only allow a few longitudinal eigenmodes. Because stable parasitic modes possess a larger spatial volume, in quasi-cw operating high-average-power solid-state lasers the longitudinal eigenmodes play a more important role than transverse ones in mode competition with the main laser. Furthermore, the polarizations are also selected by the boundary conditions, and a given eigenmode cannot possess radial polarization and azimuthal polarization components simultaneously.