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 similar to 950 and similar to 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 M-2 of 5.2 in a germanosilicate graded-index fiber.