Off-Peak Dual-Wavelength Multimode Diode-Laser- Pumped Fiber Raman Laser

We demonstrate a fiber Raman laser directly pumped by two spectrally combined multimode diode lasers at ~950 and ~976 nm. The emission wavelength becomes 1020 nm, which corresponds to the first Stokes of 976 nm. The pump separation of 270 cm^-1 is both much smaller than the Raman peak shift of 440 cm^-1 and much larger than the Raman linewidth of around 100 cm^-1, which is unfavorable for efficient Raman conversion. Nevertheless, the addition of the pump at 950 nm triples the output power compared to pumping only at 976 nm. We reach 23 W of output power with slope efficiency of 51% and beam quality M² of 5.2 in a germanosilicate graded-index fiber.