Gas-filled hollow-core fiber lasers have some natural benefits, including a high damage threshold due to the gaseous active material, high heat dissipation, and an intense light/matter interaction for small-diameter cores. This effective light/matter interaction enables efficient stimulated Raman scattering (SRS), and thus Raman gas lasers. While solid-core fiber Raman lasers have previously been developed at various infrared (IR) wavelengths, the capabilities of gas-filled Raman fiber lasers in the IR range have not been fully exploited, at least as far as multiwavelength output. Now, researchers at Technical University of Denmark (Lyngby, Denmark), Florida Polytechnic University (Lakeland, FL), CREOL, The College of Optics and Photonics, University of Central Florida (Orlando, FL), and NORBLIS IVS (Virum, Denmark) have presented a multiwavelength hydrogen-filled Raman fiber laser that can emit wavelengths spanning 1.53 to 2.4 μm at pulse powers up to 18.25 μJ; energy is shifted from one Raman line to another by tuning the hydrogen pressure from 1 to 20 bar.
The 1532.8 nm pump laser was custom-built and has a directly modulated distributed-feedback (DFB) diode-based, polarization-maintaining master-oscillator power-amplifier (MOPA) configuration; the seed oscillator produces 6.9 ns pulses at an 8 kHz repetition rate. MOPA output (with amplified spontaneous emission removed) was 640 mW (13 kW peak power, 80 μJ pulses). The light was coupled into a 5-m-long hydrogen-filled section of nested antiresonant fiber (NARF) with 80% coupling efficiency. The resulting output, which resulted from cascaded rotational SRS, was laser lines at 1683, 1868, 2100, and 2400 nm with maximum pulse energies of 18.25, 14.4, 14.1, and 8.2 μJ, respectively. The researchers foresee applications in supercontinuum generation (if the lines are broadened), multispecies gas monitoring, and photoacoustic spectroscopy. Reference: A. I. Adamu et al., arXiv:2011.06121v1 [physics.optics] (Nov. 11, 2020).
