Single-frequency Raman vortex beam enabled by a frequency-locked off-axis diamond cavity

Benefiting from the excellent optothermal properties of diamond crystals and the absence of spatial hole burning effects in stimulated Raman scattering, diamond Raman lasers hold significant advantages in achieving high-performance, single-frequency laser output. Moreover, they also demonstrate great potential in generating single-frequency vortex beams at a special wavelength. In this work, we demonstrate a single-frequency diamond Raman vortex laser by introducing simple off-axis cavity mirror misalignment into a two-mirror standing-wave diamond Raman oscillator. We calculate and analyze the output modes and transmitted signals of the diamond Raman oscillator under different off-axis conditions. Experimentally, we demonstrate resonant pumping of the diamond Raman oscillator under different off-axis conditions using the Pound–Drever–Hall frequency stabilization technique. This facilitated the generation of the single-frequency fundamental HG00 mode as well as higher-order HG01 and HG02 modes, each with low thresholds. Through extra-cavity astigmatic mode conversion, we further generated diamond-based vortex beams with topological charges of 1 and 2. Benefiting from the inherent advantages of diamond Raman lasers, this system holds significant potential for wavelength extension and power scaling of single-frequency vortex laser beams.