Low-current-density LED-pumped Nd: YAG laser using a solid cylindrical reflector

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Abstract
Results of a development program for light‐emitting‐diode (LED)‐pumped neodymium‐doped yttrium aluminum garnet (Nd: YAG) lasers highlight a significant design feature: an index‐matching method to increase the coupling efficiency of the laser. A solid‐glass half‐cylinder measuring 5.0×5.6 cm was used for index matching and also as a pumping cavity reflector. An array of twenty 0.034×0.254‐cm GaAlAs diodes, connected in series, aligned such that the emission area formed a straight line, was used to excite a 1.5×56‐mm laser rod. The interfaces between the diode array, glass half‐cylinder, and laser rod were filled with viscous fluid of refractive index n = 1.55. Experiments performed with both the glass half‐cylinder and a gold‐coated stainless steel reflector under the same operating conditions indicated that the index‐matching half‐cylinder gave 160–200% improvement of coupling efficiency over the metal reflector at various operating temperatures. For a 207‐A/cm2 driving current density the laser produced cw output power of 27 mW.