Abstract

A non-linear medium interacting with two counterpropagating pump beams is potentially unstable and can lead to a mirrorless four-wave mixing oscillation. This point was first recognized by Yariv and Pepper [1] and the observation of such an oscillation in sodium vapor has been mentioned by Tan-No et al. [2]. However, this paper was not centered on this subject and in the case of atomic vapors a detailed study of such an instability is still lacking. The situation is different for the photorefractative materials where Novikov et al. [3] have shown in which conditions a mirrorless oscillation can be observed. However, their model cannot be applied to atomic vapors. We show here that a mirrorless four-wave mixing oscillation can occur in atomic vapors for a length of the non-linear medium smaller than the value predicted before provided that the laser frequency is larger than the atomic frequency. These predictions are confirmed by experimental observations in sodium.

© 1988 Optical Society of America