High‐Energy, 4‐kW Peak‐Power, Single‐Frequency Nanosecond Fiber Amplifier at 2.7 µm

Single‐frequency (SF) pulsed lasers in the mid‐infrared (MIR) spectral region are highly demanded for applications in spectroscopy, LIDAR, and nonlinear frequency conversion, yet scaling their pulse energy and peak power while maintaining robust SF operation remains challenging. Here, we demonstrate a passively Q‐switched MIR fiber laser operating at ∼2.7 µm that achieves high peak power and pulse energy under the SF regime. The system employs a master oscillator power amplifier (MOPA) architecture. An Er 3 + ‐doped ZBLAN fiber oscillator generates stable SF seed pulses with a peak power of 118.3 W and a pulse energy of 6.3 µJ at a repetition rate of 5.58 kHz. To our knowledge, these results constitute the highest pulse energy and peak power ever reported for a passively Q‐switched SF fiber seed source operating in the MIR region. After single‐stage amplification in a cladding‐pumped ZBLAN fiber amplifier, the output peak power and pulse energy are increased to 4.44 kW and 235.4 µJ, respectively. Verified through beat frequency method and linewidth measurements, this work establishes a new benchmark for high‐power, spectrally pure MIR pulsed sources and paves the way for their advanced practical applications.