Prospects for solar-pumped semiconductor lasers

Approaches are discussed for a direct solar-pumped semiconductor laser. Efficiencies of 35% should be achievable, an order of magnitude better than the efficiency achieved by other solar- pumped lasers. The output wavelength of a semiconductor laser will be well matched to the optimum conversion efficiency of a solar cell of the same material. Solar pumped semiconductor lasers are thus an excellent candidate for space-based energy transmission. Recently several designs for such lasers have been proposed. A critical parameter is the sunlight intensity required for lasing. This threshold has been calculated to be in the range of 2500 to 10,000 times solar intensity for conventional stripe laser designs, depending on assumptions. Several approaches have been recently proposed to reduce this threshold. The calculated minimum threshold is 25 - 50 times solar concentration, and could possibly be reduced even further with use of light-trapping.