Cladding-pumped Raman laser with M^2 of 1.3 and 400 µJ first Stokes energy

Cladding-pumped Raman lasers have often been cited for their potential for brightness enhancement, but so far have never achieved high power and beam quality simultaneously. By utilizing a novel fiber geometry with a larger cladding to core ratio than current high power Raman fiber lasers for brightness enhancement (BE-RFLs), a noise-seeded Raman fiber laser pumped by a 100 ns pulsed laser with record beam quality is achieved with M^2 = 1.3 and 0.4 mJ 1st Stokes output, with an instantaneous brightness enhancement of 60. The results here support the hypothesis that the limiting factor to high beam quality in BE-RFLs is Raman conversion in the pump cladding, rather than higher order core modes as in most conventional fiber lasers.