Distributed aperture effect in laser rods with negative lenses.

Negative lenses have been ground on the ends of laser rods to increase the TEM(00) mode volume. With the negative lenses on the ends, the laser rod acts like a distributed aperture. The distributed aperture radius and its effect on the useful volume of the laser rod are calculated. The mode radius and the diffraction loss for a laser rod with negative lenses ground on the ends are presented as a function of laser rod focal length and the Fresnel number.