Ray-transfer-matrix approach to unstable resonator analysis

A parametric analysis of unstable resonators is described. The resonator is mathematically represented by an appropriate ray-transfer-matrix, and changes in Gaussian beam parameters are calculated after propagation through the optical structure. The results highlight an inherent selective property that presents an effective loss mechanism for divergent radiation. This selective property is shown to be dependent on the resonator parameters of optical magnification and confocal length error. The analysis concludes that the initially backward-propagating radiation during the prelasing period is important in establishing low threshold and good beam quality in confocal unstable-resonator lasers.