Threshold reduction and mode selection with uncoated Raman crystal acting as a low-finesse cavity

We report a stimulated Raman scattering threshold reduction by a factor of ∼4 using a simple uncoated SrWO₄ crystal with plane/parallel faces pumped by 1.5 mJ, 11 ns single-frequency pulses at 532 nm. The weak etalon effect is sufficient to shape both the spatial and spectral characteristics of the output Raman beam. The Raman signal tends to be single-frequency close to threshold, which might be an interesting way to further seed Raman amplifiers for high-energy Fourier-limited pulses at particular visible or near-infrared wavelengths.