Lateral displacement of the mode axis in a misaligned Porro prism resonator.
The lateral shift of the mode axis in a misaligned Porro prism resonator is analyzed. A method to find the tilted mode axis in a misaligned Porro prism resonator is introduced. Expressions for the displacement of the mode axis are deduced. They predict that the lateral displacement of the mode axis is proportional to the horizontal misalignment angle beta and highly dependent of the prism azimuth angle theta. Experimental results obtained agree well with theory.
Transverse modes in porro prism resonators
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.
Choice of Mirror Curvatures for Gas Laser Cavities
A brief review of transverse mode structure in various curved mirror laser cavities is given. Cavities considered are those consisting of two concave mirrors, a concave and a plane mirror, and a concave and a convex mirror. The volume of the TEM00 mode in the various cavities is discussed, and the alignment tolerance on the mirrors is considered. It is shown that the maximum volume of the TEM00 mode in the near-hemispherical cavity is roughly one-third of the volume in the plane-parallel cavity, but that for a given mode volume, the near-hemispherical cavity is the easiest of all curved mirror cavities to align. It is suggested on the basis of the above consideration that the near-hemispherical cavity is the most practical cavity to use in a laser.