Doppler-induced unidirectional operation of a continuous-wave Raman ring laser in H2. 
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.