nLight proposes to develop high-power, high-efficiency laser diodes emitting at 1907nm. Performance is expected to improve from the current state-of-the-art technology at 15C of 20% electrical-to-optical (E/O) conversion efficiency and 11.5W continuous-wave power (CW) to 25% E/O efficiency and 18W of CW power at the conclusion of Phase I. At the conclusion of Phase II, these values are expected to improve to 38% E/O efficiency and greater than 35W CW power. Quasi-CW power will be >>100W per laser bar. Such lasers meet the brightness and power requirements for the direct pumping of the quasi 4-level 5I7 to 5I8 transition in singly-doped Ho:YAG lasers. Compared to the diode-pumping of Thulium-sensitized Ho:YAG, direct diode pumping of Ho:YAG takes advantage of Holmium's much larger emission cross section, the absence of Ho:Tm up conversion, and Ho:YAG's large energy storage lifetime. Direct diode pumping of Ho:YAG also results in decreased system size, weight and complexity and an improvement in overall system efficiency when compared to pumping with a diode-pumped Th:YAG laser, all critical metrics for space and airborne platforms. This work could be extended to 18xxnm and 20xxnm quite readily with comparable power and efficiency performance.
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