Efficient picosecond traveling-wave Raman conversion in a SrWO4 crystal pumped by multi-Watt MOPA lasers at 1064 nm

Raman conversion with a 50-mm-long SrWO4 crystal in a single-pass, traveling-wave setup has been investigated in both purely steady-state and transient stimulated Raman scattering (SRS) regimes. For steady-state SRS experiment, we employed as a pump source a Q-Switched master oscillator power amplifier (MOPA) laser system at 1064 nm, delivering 325 μJ, 550-ps-long pulses with diffraction limited beam quality and high spectral purity. At 2-kHz repetition rate, we obtained up to 90 μJ pulse energy and 250 ps pulse duration at 1180 nm, with a conversion slope efficiency close to quantum limit. To approach the transient SRS regime, we pumped the same crystal with 16-ps-long pulses from a hybrid MOPA laser system based on a mode-locked Yb-fiber oscillator followed by a diode-pumped bulk Nd:YVO4 power amplifier. At the maximum incident pump average power of 3.75 W, we obtained 1.4 W at the first Stokes Raman-shifted wavelength of 1180 nm (37 % optical-to-optical conversion efficiency), with 15 ps pulse duration and 70 % conversion slope efficiency.