temperatures and high average power is the Nd:glass-fiber bundle laser. Early experiments look very promising. Approximately 20 watts of power were generated at a solar simulator concentration of 2000 [3], However, each fiber in the bundle had to be sealed water tight, and power degradation occurred when water covered the emitting ends of the fibers. Other geometries for solar-pumped solid-state lasers include thin slabs which offer both thermal and power extraction advantages over the traditional rod geometry. Measurements have been made on the fraction of organic iodide lasant molecules lost in the gas phase by dissociation. The fraction estimated was of the order of 10~6. Thus such molecules can participate in lasing approximately 106 times. On the other hand, except for a catastrophic accident, the ion in a solid host can lase an almost unlimited number of times. Research is continuing on gas and solid-state, solar-pumped lasers to define solar- pumped lasing characteristics, beam quality, and the potential for continuous high average-power operation. 2.2. Electrically Driven Semiconductor Diode Lasers Semiconductor diode lasers are being developed for commercial applications ranging from telephone communications to optical readers for supermarkets. Recently diodes made of GaAs-like materials have achieved 70% electrical-to-laser power conversion efficiency in the laboratory [4]. Industrial processes are producing diodes with over 30% power efficiency and several watts of CW (continuous wave) power per diode array. Their emission wavelength is near 0.85 //m. These diodes have excellent characteristics for space applications. They are high- current, low-voltage devices, and thus will require a minimum of power-conducting circuitry when used with solar cells. Semiconducting devices similar to these lasers generally have long operating lifetimes. However, laser diodes are very temperature sensitive. They need to operate near 300 K with a temperature stability of better than
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