Actively pulse shaped hybrid rare-earth-doped silica fiber/Ho3+:YAG MOPA system at 2048 nm

In this study, an efficient hybrid fiber and solid-state master oscillator power amplifier (MOPA) system is introduced. This system is composed of an actively pulse-shaped Ho3+- and Tm3+-doped silica fiber MOPA at 2048 nm. A subsequent Ho3+:YAG power amplifier stage enables the efficient scaling of the pulse energy. By utilizing a novel cascaded crystal configuration, designed with a numerical simulation model, the Ho3+:YAG stage has been optimized for operation at 2048 nm wavelength. This operation at wavelengths much shorter than the typical emission peaks around 2090 nm showcases the possibility of using Ho3+:YAG as a broadband amplification medium. With a signal input power of 24 W at the crystal stage, we achieved an output power of 81.6 W. This corresponds to a gain of 5.3 dB with a slope efficiency of 68 % with respect to the launched pump at 1908 nm. The fiber/bulk hybrid approach enabled an increase in the energy of the rectangular-shaped nanosecond pulses from an initial 0.48 mJ to 1.63 mJ at 50 kHz, surpassing the pulse scaling limitations for standard thulium-doped silica fibers.