Selection and generation of multipass modes in an open resonator.

The original numerical wave model of the open resonator has been employed in the investigation of conditions for multipass mode generation. It is shown that for Fresnel numbers larger than unity, multiple reflections of radiation from the stable resonator mirrors lead to sustained quasi-stationary oscillations which are indicative of multipass mode generation. Various types of ray trajectories have been considered at the paraxial resonance conditions. Trajectory selecting techniques are suggested to provide the high quality output beams at large Fresnel numbers. The results of numerical experiments on amplitude-phase distribution of output radiation are presented for the suggested schemes.