GdVO₄ Raman laser of Lorentzian linewidth less than 3 Hz

Raman lasers are emerging as promising sources of optical frequencies with low phase noise. Studies so far have centered on diamond as the Raman gain medium, a material well suited to stable single longitudinal mode operation. Here we report a single longitudinal mode GdVO₄ Raman laser based on a doubly resonant cavity stabilized to the pump frequency using Pound-Drever-Hall locking and providing output wavelengths at 1164 nm and 1174 nm. Frequency noise measurements at high Fourier frequencies indicate a Lorentzian linewidth below 3 Hz, with the observed value limited by technical noise in the laser cavity and the linewidth measurement system. To our knowledge, this represents the narrowest linewidth reported for any Raman laser and demonstrates that non-diamond Raman materials can support narrow linewidth operation and a greater diversity of output wavelengths.