A doughnut-shaped Nd:YAG solar laser beam with 4.5 W/m2 collection efficiency

Abstract

In this paper, a doughnut-shaped solar laser beam from a Nd:YAG rod pumped through a heliostat-parabolic mirror system is reported. A solar laser head was composed of a fused silica liquid light guide lens and a conical pump cavity, within which a 4 mm diameter, 35 mm length Nd:YAG single-crystal rod was efficiently end-side-pumped. Multimode solar laser power of 24 W was measured by adopting a short laser resonant cavity, attaining 6.4% slope efficiency. The influence of the radius of curvature of the output mirror and laser resonant cavity length on the laser output performance were studied. By operating the laser resonator close to the edge of the optically stable region, record 4.5 W doughnut-shaped solar laser power was achieved, corresponding to 4.5 W/m2 collection efficiency, which is 1.67 times higher than previous record from a side-pumped grooved Nd:YAG laser rod. A four-petal like Gaussian solar laser beam was also produced for the first time. This technique required no additional optical element in the resonator, reducing thus laser power losses and system complexity.