Doppler-Induced Unidirectional Operation of a Continuous-Wave Raman Ring Laser in H 2

We demonstrate stable operation of a diode-pumped cw Raman ring laser in diatomic hydrogen gas. Doppler-induced asymmetry between the the forward and the backward Raman gains leads to inherent unidirectional operation in the forward direction without intracavity optical elements. Use of the ring-cavity geometry dilutes the deleterious effects of thermal lensing and significantly reduces optical feedback to the pump laser.