Cryogenically-cooled eyesafe laser diode arrays for resonant pumping of Er-doped gain media

High-power solid state lasers operating beyond 1300-nm have been proposed as “eye-safer” sources in many applications. Erbium-doped solid state lasers provide an attractive gain medium due to emission at eyesafe wavelengths, and the potential for ultra-low quantum defect pumping by diode lasers operating around 1532-nm. It has been shown that cooling the solid state crystalline gain medium to cryogenic temperatures provides significant advantages in efficiency and power scaling. To date, these lasers are typically pumped by diode laser modules operating at or near room-temperature. It is well-established that cryogenic cooling of diode lasers can greatly improve efficiency and power. However, to fully realize these benefits, the diodes must be specially designed for operation at cryogenic temperatures. In this work, we propose diode laser arrays operating at ~1532-nm which are specifically designed and optimized for operation at 77K. Under the proposed program, nLight will design, grow, fabricate, test, and deliver to the Army Research Laboratory a series of conductively-cooled 1532-nm 100W, 65% efficient 1-cm diode laser bars for evaluation in cryogenic solid state laser pumping experiments. As an option to the program, nLight will also assemble test and deliver to the Army Research Laboratory a fiber-coupled conduction-cooled 100W, 60% efficient pump module.