The quasi-stationary wave patterns inside a two-mirror optical resonator are evaluated as the sum of a progressive and a regressive wave by assuming the mirrors to be illuminated by the fundamental mode of the resonator at a resonance frequency. The progressive and the regressive waves are also evaluated in the case of the first-order mode. Calculations are made for an infinite-strip Fabry-Perot resonator, as well as for a cylindrical and a confocal resonator, with Fresnel number N = 1.
F. Pasqualetti and L. Ronchi, "Quasi-Stationary Wave Patterns Inside Infinite-Strip Open Resonators," Appl. Opt. 10, 2488-2494 (1971)