Pound–Drever–Hall stabilized single-frequency diamond Raman laser with sub-10 kHz linewidth

Benefiting from the exceptional properties of diamond crystals and the absence of spatial hole burning in stimulated Raman scattering, diamond Raman lasers (DRLs) are effective materials for achieving a single longitudinal mode laser output at specific wavelengths. The use of resonant pumping techniques can yield a low-threshold single longitudinal mode DRL output. However, the polarization dependence of the Raman gain in diamond and the birefringence induced by high-power lasers affect the output stability and single longitudinal mode characteristics of Hänsch-Couillaud (HC) frequency-stabilized DRLs. To achieve a highly stable, narrow-linewidth DRL output, this study, for the first time, to the best of our knowledge, employed polarization-insensitive Pound-Drever-Hall (PDH) frequency stabilization technology to resonantly pump an external cavity standing-wave diamond Raman oscillator. By using a narrow-linewidth 1064 nm laser as the pump source and locking the cavity length to the pump frequency, a single longitudinal mode 1240 nm first Stokes laser output of 1.3 W was achieved at a maximum pump power of 8 W. The corresponding center wavelength drift and the RMS of output power over 10 min were 25 MHz and 1.87%, respectively. Additionally, the linewidth of the Stokes laser at a maximum output power is 8.8 kHz, representing the first experimental characterization, to our knowledge, of DRL linewidth under resonant pumping conditions. This work demonstrates that DRLs possess significant advantages and potential for achieving a high-power, high-frequency-stability, narrow-linewidth laser output.