Abstract
The diffraction losses of the cylindrical confocal resonator having a circular coupling aperture in the center of one of the resonator mirrors have been calculated over the range of resonator Fresnel numbers0 \leq N_{b} \leq 1.6by the numerical iteration technique of Fox and Li. The specific paths by which energy is diffracted from the resonator have also been investigated and a class of equivalent resonators found that maximizes the energy diffracted through the aperture for a given value of total diffraction loss.