A mode-locked, sun-pumped Nd:YAG laser

The finite lifetime of conventional pump sources and the limited power available in a spacecraft make solar pumping of a space-borne optical communication laser an attractive approach. This paper describes a Nd: YAG laser in which solar energy is used directly to produce the population inversion. Sunlight is collected by a 24-inch diameter mirror and focused into the end of the laser rod. This "end pumping" configuration permits "side pumping" by lamps or light-emitting diodes when the sun is not visible from the satellite. The laser rod is soldered to a heat sink and cooled by direct conductive cooling, a technique which is compatible with spacecraft application. A multi-nlode output of 1.5 watts has been obtained with this laser. A specially-designed, low-loss LiNbO3phase modulator is used to mode lock the laser and produce an output pulse-train which is suitable for use in a pulse-code-modulation optical communication system.