Passively Q-switched fiber laser that uses saturable Raman gain

Operation of a short all-fiber passively Q-switched Raman laser pumped by a continuous-wave laser diode is experimentally demonstrated. The passively switched fiber laser consists simply of a double-clad ytterbium-doped silica fiber that is spliced directly to a moderately germanium-doped silica fiber. The placement of the Ge-doped silica fiber within the fundamental (Raman pump) cavity allows interplay between fundamental and Stokes fields to take place, which leads to saturation of the Raman gain as a result of pump depletion. Pulse widths of 70 and 60 ns at the first and second Stokes wavelengths of 1168 and 1232 nm, respectively, are produced at a stable 588 kHz repetition rate.