Characterization of a single-frequency-pumped continuous-wave extracavity diamond Raman laser

In this paper, we report a characterization of an external cavity cw diamond Raman laser pumped by a single frequency fibre laser. The diamond was pumped using a seeded (linewidth ≈5 MHz) TEM₀₀ mode linearly polarized Yb based fibre laser (IPG Photonics) operating at 1064 nm focused to a diameter of about 40 μm. The diamond faces were antireflection coating for pump and Stokes wavelengths, and the output coupling was 0.5%. To spatially mode-match the pump to intracavity Stokes field the resonator was nearly concentric. The laser threshold was 10 W, similar to that observed for the multimode laser (11 W). The 1240 nm output power increased linearly with further increases in input power up to 15 W at a maximal available pump power of 42 W. As far as we are aware, this is the first demonstration of fibre laser pumped crystal Raman and the highest cw power yet reported for any crystal Raman laser. The slope and conversion efficiencies were 46% and 35%, respectively. The output spectrum was investigated as a function of output power and was found to transition between single and multi-longitudinal mode output depending on the power level. Strategies for enabling efficient and stable conversion to SLM output will be discussed.