Collisionally Induced Narrowing of the Longitudinal Relaxation Linewidth in Nearly Degenerate Four-Wave Mixing

This paper reports the observation of collisionally induced spectral narrowing of the longitudinal relaxation linewidth with use of the nearly degenerate four-wave mixing process. A theoretical model, which takes into account strong velocity-changing collisions for the population and phase-interrupting collisions for the optical coherence, leads to a good qualitative understanding of this new effect.