Watt-Level Nanosecond 4.42- $\mu$ m Raman Laser Based on Silica Fiber

We report the demonstration of a 4.42-μm silica-fiber-based Raman laser delivering a record average output power of 1.4 W and operating in a single transversal mode. The Raman laser is based on a hydrogen-filled hollow-core silica fiber, which is pumped by a nanosecond erbium-doped fiber laser at 1.56 μm. In spite of a large quantum defect of a 1.56-4.42-μm conversion, the Raman laser demonstrates no heat-initiated problems. Due to the implementation of a linearly polarized pump and virtually all-polarization-maintaining configuration of the Raman laser, the quantum efficiency has reached 53%, which is a theoretical limit imposed by optical losses (1.1 dB/m) at 4.42 μm in a state-of-the-art revolver hollow-core silica fiber. The developed laser demonstrates the prospects of gas fiber Raman lasers to serve as pump sources for high-power supercontinuum generation in the mid-infrared spectral range. Such sources can find numerous scientific and biomedical applications.