Silica-based fiber Raman laser at > 2.4  μm.

Raman laser generation at the long wavelength transmission edge of silica fiber is explored. Numerical simulation reveals that high efficiency 2nd Stokes Raman laser operation around 2.5 μm is feasible with highly Ge-doped silica fiber as the gain medium and pulsed 2-μm fiber laser as the pump source. Based on the spontaneous cascaded Raman amplification process, 0.30-W laser at 2.43 μm is obtained with an optical efficiency of 16.5% pumped at 2008 nm. And 0.15-W laser at 2.48 μm is achieved with an optical efficiency of 7.9% pumped at 2040 nm. To the best of our knowledge, the results represent the longest wavelength operation of silica-based fiber laser.