Details Of The Evolution Of The Output Divergence From Positive-Branch Confocal Unstable Resonators

Abstract

In an unstable laser resonator, spontaneous emission, which is emitted by the gain medium just as the laser resonator rises above threshold, propagates around the resonator while being coherently amplified and eventually becomes the outcoupled light. The approximate output pattern of pulsed, collimated unstable resonators can be determined by the sizes of and distance between the output aperture and the image of the spontaneous emission source, as viewed from the output aperture by looking back through the optical chain of the unstable resonator. In this paper, a detailed analysis of the time dependent output pattern of two common, positive-branch unstable resonators is presented in geometrical optic regime. The effect of a dot outcoupler and multiple internal apertures on the output pattern is investigated and some simple rules for analyzing other resonators are also presented.