Role of the pumping beam's shape in microchip lasers

A technique for the generation of the cylindrical symmetry Laguerre-Gaussian fields TEM*/sub p,l/ with p = 0 and specified values of l in a fiber-coupled diode end-pumped solid-state laser is reported. The key novelty is to produce a doughnut-shaped pump-profile by defocusing a standard fiber-coupled diode. The experimental results demonstrate that the stable transverse-mode pattern near the pump threshold is usually a LG TEM/sub 0,l/ mode with the distribution cos/sup 2/ l/spl theta/ (or sin/sup 2/ l/spl theta/ ) in azimuthal angle, having 2l nodes in azimuth.