Transverse modes in porro prism resonators

Abstract

This dissertation consists of two main sections. The first is a review of laser resonators using spherical mirrors, and incorporates a physical optics numerical model of a Fabry-Perot laser resonator without gain. The output of this model, which includes spot sizes, loss, and transverse mode formation, is compared to the parameters calculated using published analytical results. This comparison serves as a verification of the numerical methods used, as well as a frame of reference for the model of a Porro prism resonator which follows in the second section. The second section proposes a new method for analysing Porro prism resonators. The analysis incorporates both geometric as well as physical optics concepts, with the prisms modelled as rotating elements with amplitude and phase distortions. This yields expressions for the orientation of the loss at the apex of each prism, and as well as the number of petals in the “petal-pattern” beam structure commonly observed from Porro prism lasers. These expressions are included in a numerical model, which is first used to verify the development of the characteristic petal-pattern. Next, the numerical model is used to investigate the development of the beam structure, in both time and space, in crossed Porro resonators with a range of Fresnel numbers and stability parameters. This leads to some new insight into the transverse modes of these lasers.