Gain-switched all-fiber 3.5 μm laser with high pulse energy

We report the demonstration of an all-fiber pulsed laser at 3.5 μm based on gain-switching scheme. The cavity, formed by splicing two fiber Bragg gratings to a piece of Er-doped fluoride fiber, is dual-wavelength pumped by a pulsed 2 μm fiber laser and a continuous-wave 0.98 μm laser diode, and delivers an average output power of 1.22 W. Benefited from the short cavity length and high pump energy, a maximum output pulse energy of 61 μJ with short width of 162 ns, is obtained at 20 kHz repetition frequency, contributing to a high peak power reaching 354 W. The demonstrated laser combines high power, high energy, short width with long-term stability, offering a compact mid-infrared platform in applications such as sensing, spectroscopy, and material processing. Moreover, methods of further improving the output energy and suppressing the trailing pulses were also discussed based on a developed transient model.