High-order random Raman lasing in a PM fiber with ultimate efficiency and narrow bandwidth

TLDR

Random Raman lasers in scattering media, particularly single‑mode fibers using Rayleigh backscattering, can produce high‑quality unidirectional beams but suffer from degraded spectral and polarization performance at higher powers and Stokes orders. The study demonstrates linearly polarized cascaded random Raman lasing in a polarization‑maintaining fiber. The cascaded random Raman laser achieves near‑constant quantum efficiencies of 79–83 % across the first three Stokes orders, maintains >22 dB polarization extinction, exhibits ~1–3 nm bandwidths largely independent of 1–10 W power, and shows no degradation with increasing order, supported by a comprehensive theoretical model.

Abstract

Random Raman lasers attract now a great deal of attention as they operate in non-active turbid or transparent scattering media. In the last case, single mode fibers with feedback via Rayleigh backscattering generate a high-quality unidirectional laser beam. However, such fiber lasers have rather poor spectral and polarization properties, worsening with increasing power and Stokes order. Here we demonstrate a linearly-polarized cascaded random Raman lasing in a polarization-maintaining fiber. The quantum efficiency of converting the pump (1.05 μm) into the output radiation is almost independent of the Stokes order, amounting to 79%, 83%, and 77% for the 1(st) (1.11 μm), 2(nd) (1.17 μm) and 3(rd) (1.23 μm) order, respectively, at the polarization extinction ratio >22 dB for all orders. The laser bandwidth grows with increasing order, but it is almost independent of power in the 1-10 W range, amounting to ~1, ~2 and ~3 nm for orders 1-3, respectively. So, the random Raman laser exhibits no degradation of output characteristics with increasing Stokes order. A theory adequately describing the unique laser features has been developed. Thus, a full picture of the cascaded random Raman lasing in fibers is shown.