Polarization dynamics of a diamond Raman laser governed by local stress and pump polarization perturbation

Stress in diamond crystals is a critical factor affecting Raman gain and the polarization state of the output Stokes. This study systematically investigates the multi-field coupling among residual-stress-induced birefringence in diamond, initial pump ellipticity, and stimulated Brillouin scattering (SBS). By combining theoretical simulations, division-of-focal-plane polarization imaging, and Raman laser experiments, we elucidate the mechanisms responsible for the stepwise evolution of the Stokes polarization direction. In high-stress regions, birefringence-induced phase distortion dominates the polarization dynamics, leading to abrupt polarization switching. In low-stress regions, SBS acts as a parasitic loss channel that forces polarization-mode transitions and limits power scaling. The results further confirm that even slight pump polarization perturbations can degrade the Raman output polarization state, reduce the effective gain, and increase the laser threshold. These theoretical and experimental findings provide practical guidance for overcoming performance bottlenecks in diamond Raman lasers, screening high-quality crystals, and developing efficient coherent light sources with precisely controllable polarization states.