Mode discrimination and coupling losses in rectangular-waveguide resonators with conventional and phase-conjugate mirrors

Abstract

Coupling losses in a waveguide-laser resonator are considered for an arbitrary waveguide mode. For a rectangular waveguide the coupling efficiency is shown to be expressed in terms of a onefold integral, which can be evaluated in a closed form for three practical cases of interest corresponding to plane-parallel, half-concentric, and semiconfocal geometries. The results are used to discuss the extent of mode discrimination as well as the choice of optimum parameters for a compact waveguide-resonator design. The case of a phase-conjugate mirror is also considered. When an effective finite mirror size is used, a phase-conjugate waveguide resonator is shown to be capable of transverse-mode discrimination while providing low coupling losses for the fundamental waveguide mode.