Enhanced stability of a single-longitudinal-mode diamond Raman laser enabled by pump-wavelength locking

To overcome the insufficient long-term stability of conventional Raman lasers, we demonstrate a single-frequency diamond Raman laser enabled by a pump-wavelength locking strategy. A three-mirror V-shaped cavity pumped by a 1064 nm fiber laser (6 kHz linewidth) provides single-longitudinal-mode (SLM) output at 1240 nm using Pound-Drever-Hall (PDH) stabilization. We further find that eliminating active temperature control of the diamond crystal suppresses rapid thermal perturbations and improves short-term stability. To compensate thermally induced slow cavity-length drifts, we implement a dual-loop feedback architecture that employs a fast PID loop acting on the pump wavelength and a slow PID loop driving a cavity piezoelectric transducer (PZT). Specifically, the fast loop tunes the pump wavelength via laser-current modulation, while the slow loop stabilizes the cavity length by regulating the PZT voltage. With 22 W pump power, the system produces 2.5 W SLM output with a linewidth of ∼2.9 kHz. The locked Raman laser exhibits an output power instability below 1.59% and a wavelength drift below 87 MHz, demonstrating markedly improved long-term operational stability. Unlike mainstream cavity-length locking techniques, our approach exploits the PDH error signal to directly lock the pump wavelength, providing a high-performance and wavelength-scalable route to highly stable single-frequency laser sources.