Abstract

Abstract Random Raman lasing in multimode graded-index fibers is accompanied by sufficient improvement of the output beam quality in comparison with that for pump radiation resulting in brightness enhancement, however the threshold pump power is rather high. Here we study an opportunity to reduce Raman threshold and to obtain random Raman lasing in laser diode pumped multimode graded-index fiber with enhanced backscattering on artificial fs-inscribed random structures of Rayleigh type (random points) or an array of short fiber Bragg gratings randomly spaced in longitudinal and transverse directions. Another goal is to test scaling capabilities for output power of random Raman finer laser based on natural Rayleigh scattering with higher pump powers. In both experiments, 100-µm graded fibers with UV-laser inscribed FBG (R∼90%) are explored and some kinds of unstable behavior with specific modal dynamics is observed and analyzed.