Abstract

The statistical properties of spontaneously generated Raman solitons are of significant interest because they reflect the statistics of the photon vacuum. These solitons arise when the fluctuating vacuum nearly vanishes at a space-time point (i.e., its expectation values nearly vanish). At such a point, a near phase reversal takes place, so that molecules that are phased to absorb incident radiation instead emit radiation at that frequency; with subsequent phase disruption caused by molecular collisions, phase locking is reestablished, and the radiation is again absorbed. The sequence of pump-frequency absorption, emission, and absorption produces a peak in the pump signal whose width is approximately the mean collision time. Such peaks are shaped by further propagation and show remarkable stability. Although they eventually decay, many survive into the macroscopic regime and may be detected. Specifically, using parameters consistent with ongoing experiments, we have found that solitons having peak intensities greater than one-tenth the pump-pulse maximum can be detected in ~12% of the pulses sent through the Raman medium. The delay time distribution of the solitons decays quasiexponentially, while the soliton height distribution appears to be bimodal.

© 1989 Optical Society of America