Efficient power-scalable and diffraction-limited GaAs diode lasers

Diode lasers now deliver very high powers at high efficiency, with ~70% electrical-to-optical conversion efficiency demonstrated by several groups from bars with powers of 100 W or greater. However, these devices are incoherent, multi-mode sources that cannot be focused effectively on a distant target and are not suitable for use as a directed energy weapon. Current directed energy designs rely on the use of “brightness converters” – the light from such high efficiency diodes is used to pump another laser medium with high quality single mode output, such as rare earth doped solid-state crystals, glass fibers, and complex flowing alkali gas cells. These brightness converters add cost and complexity and sacrifice efficiency – wasting 50% or more of the injected diode laser energy by turning it into heat. The ideal situation would be to eliminate the brightness converter and use diode lasers directly. This would enable high energy laser (HEL) systems with dramatically reduced cost, size, weight, and power (CSWaP) requirements. However, the power and efficiency of diffraction-limited diode lasers significantly lags that of the broad area pump diodes. A significant increase in the reliable power, efficiency, and beam quality of diffraction-limited semiconductor lasers is necessary to enable HEL systems based on direct diode technology. In this proposed effort, Freedom Photonics seeks to develop and demonstrate a manufacturable, high power, high efficiency, diffraction-limited, and highly-reliable diode laser device technology. By the end of Phase 2, we will demonstrate and deliver prototype GaAs-based single emitter lasers capable of producing high output power with E/O efficiency comparable to current multi-mode lasers, with a nearly diffraction-limited single mode output beam and excellent reliability. The primary purpose of the proposed Phase 1 effort will be to 1) demonstrate viability of the proposed laser approach to simultaneously demonstrate high power, with good efficiency, and nearly diffraction-limited beam quality, 2) to quickly assess key design aspects which will require detailed investigation during the Phase 2 effort, and 3) to develop a strategy for rapid qualification and injection of our device technology into the Department of Defense High Energy Laser applications. To these ends, the Phase 1 effort can be seen as means for mitigating technical, schedule, and business risk of the entire development program. Approved for Public Release | 20-MDA-10643 (3 Dec 20)