Abstract

A numerical model was developed that propagates beams inside cavities containing gain, separate nonlinear media, and apertures. The model, using Hankel transforms, calculates radial field distributions in cavities and rigorously calculates losses for given intensities in ring or standing wave lasers. We investigated the influence of aperture position, aperture size, nonlinear crystal position, and nonlinearity of the crystal on laser losses versus intracavity power. The model was used to optimize the design of an n₂ mode-locked laser. Although previous works show a linear relation between intracavity power and losses, we found large deviations even at low power when using high-n₂ crystals. Increased power results initially in a decrease of the losses, but eventually the losses increase even above the initial level. The minimum loss level is critically dependent on crystal and aperture positions. For an 8 mm CdS crystal used as a nonlinear medium, the losses vs. power slope was increased by a factor of 400 with respect to a cavity utilizing a single Ti-sapphire crystal, which is crucial for low power self starting mode-locked lasers.

© 1992 Optical Society of America