Abstract

CW Raman lasing in multimode graded-index (GRIN) fibers directly pumped by high-power 9xx-nm multimode laser diodes (LDs) attracts recently great deal of attention due to the opportunity to efficiently generate laser radiation in the wavelength range of 940-980 nm, where generation of conventional Yb-doped fiber lasers is hardly possible. It has been shown that the beam quality is improved from M²~30 for the LD pump to M²~2 for the Stokes beam generated in the cavity based on either special fiber Bragg gratings [1] and/or random distributed feedback via natural Rayleigh scattering in multimode fiber [2], but in the latter case the Raman threshold is high (~500W). Here we study an opportunity to obtain random Raman lasing in multimode diode-pumped GRIN fiber with enhanced backscattering on artificial fs-inscribed random structures of Rayleigh type (random points) or an array of short FBGs randomly spaced in longitudinal and transverse directions.

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