Doppler-induced unidirectional operation of a CW Raman ring laser

Summary form only given. Lasing was recently achieved on a third-order nonlinear optical transition in gaseous hydrogen. The researchers used a highly stabilized, frequency-doubled Nd:YAG laser to pump the Q(1) vibrational Raman transition in diatomic hydrogen gas, which was substantially enhanced by a doubly-resonant high-finesse Fabry-Perot cavity (HFC). The transition was pumped with diode lasers shortly thereafter, which highlighted the usefulness of this technique for generating broadly tunable, narrow linewidth laser radiation throughout the near infrared. However, these systems utilized exclusively linear Raman laser resonators. By exploiting a Doppler-induced Raman gain anisotropy between the forward and backward directions, we demonstrate what is to our knowledge the first unidirectional Raman ring laser. We are unaware of other ring laser systems that utilize this inherent anisotropy in a predominantly homogeneous gain medium.