Abstract

Hermite-Gaussian modes have formed the basis for the analysis and understanding of stable-cavity lasers for many decades. These modes tend to be highly paraxial and have low round-trip loss but often do not exploit the full volume of the gain medium. On the other hand, unstable-cavity lasers utilise diverging light wavefronts for high gain extraction, leading to strong periodic aperturing effects and high-loss modes. The transverse structure of these modes is determined, to a large extent, by the detailed symmetry of the aperturing element, resulting in mode patterns which are radically different from those of conventional stable-cavity lasers. However, to date, only strip-type and circular transverse geometries have been considered, since then the problem reduces to one-dimension. We have undertaken the first investigations of the transverse modes of unstable-cavity lasers with truly two-dimensional aperture symmetries. Our studies have concentrated on cavities with triangular apertures and work is currently underway on the generalisation of these results to encompass N-sided polygon and variable-angled rhombus symmetries. A full update of results from experimental, semi-analytical and numerical work will be presented.

© 1998 IEEE