Effect of cavity mode matching on the output performance of external-cavity diamond Raman oscillators

Mode matching between the pump beam and the cavity eigenmodes plays a critical role in determining the beam quality and conversion efficiency of laser systems. However, compared to population inversion lasers, research on mode matching in Raman lasers has received less attention. Here, we investigate mode-matching characteristics in an external-cavity diamond Raman laser (DRL), leveraging the superior thermal properties of diamond. By employing quasi-continuous pump sources exhibiting significantly different beam qualities, high beam quality first Stokes laser output was achieved across a wide range of cavity length adjustments designed to modify the intra-cavity mode matching. The dynamic cavity length adjustment range reached 6 mm. Under the condition of a pump beam M² factor of 4.5, a beam quality improvement exceeding fourfold was attained. The compatible mode-matching ratio range between the pump beam and the resonant modes was found to be 0.54 to 1.20. Furthermore, the impact of different cavity lengths on the stable laser output power was analyzed. This work demonstrates the outstanding performance of the DRL in generating high beam quality output, along with its high tolerance to variations in pump beam quality and cavity length. The investigation of Raman cavity mode matching provides crucial guidance for laser design.