High-efficiency LD-pumped all-fiber Raman laser based on a 100 µ m core graded-index fiber

We demonstrate a high-power, high-efficiency Raman laser based on a 100 µ m core graded-index (GRIN) fiber directly pumped by 915 nm multimode laser diode modules in all-fiber configuration. Optimization of GRIN fiber length and pumping scheme was performed. As a result, 62 W of CW power has been obtained at a wavelength of 954 nm with a slope efficiency of 85%. The joint action of Raman clean-up effect and mode-selection properties of special fiber Bragg gratings inscribed in the central part of the GRIN fiber core results in significant beam quality enhancement for the generated Stokes beam ( < 3) in comparison with that of the pump radiation ( > 30). In addition, the exact value of the operating wavelength near the Raman gain maximum was varied. To the best of our knowledge, this is the first study of the impact of a Raman gain spectral profile on the power, spectrum and beam quality parameter M 2 of multimode Raman laser. It appears that they very much dependent on the spectral region of Raman gain at which we work, when the wavelength is selected by a fiber Bragg grating inscribed in a multimode GRIN fiber.