Raman soliton generation from laser inputs in SRS

Farrès P. Mattar, David J. Kaup, George R. Harrison

R. C. Swanson, David C. MacPherson, John L. Carlsten

In our studies of soliton formation in stimulated Raman scattering (SRS), we have discovered that a fully quantum mechanical theory predicts large shot-to-shot fluctuations in the SRS power spectrum, which leads to soliton decay. This theory, which includes a Langevin operator to simulate collision-induced fluctuations and maintain operator consistency, can be used to generate the statistics of the macroscopic SRS output. We have also studied a simpler model which uses a random vacuum field as an input to the semiclassical SRS equations. The vacuum field was numerically generated by summing a set of electromagnetic field modes that spanned the collisional Raman linewidth. Each mode was separated in frequency by less than the resolution of the system and given a random phase for each shot. Despite the lack of Langevin terms, the shot-to-shot variations and two-frequency correlation function from the simple approach were essentially indistinguishable from the fully quantum mechanical theory. This suggests that a simulation of SRS from spontaneous emission does not always require Langevin terms in the quantum noise.

M.O. Baumgartner, Fritz Kurt Kneubühl

Stimulated Raman scattering is a nonlinear process, that has been studied extensively by many groups. Nevertheless, the presence of soliton-like pulses in the depletion region of the pump pulse is not yet completely understood. The origin of such spontaneous solitons is the rapid phase variation of the Stokes field induced by the quantum fluctuations of the electromagnetic field in vacuum. With the aid of a pulsed CO/sub 2/ laser system including a fast plasma shutter we have observed the first spontaneous Raman solitons in the forward stimulated Raman scattering (SRS) by the far-infrared-active laser gas NH/sub 3/.

John L. Carlsten, David C. MacPherson

Jérôme J.-P. Leon, А. В. Михайлов

Stimulated Raman scattering of a laser pump pulse seeded by a Stokes pulse generically leaves a two-level medium initially at rest in an excited state constituted of static solitons and radiation. The soliton birth manifests as sudden very large variations of the phase of the output pump pulse. This is proved by building the IST solution of SRS on the semi-line, which shows moreover that initial Stokes phase flips induce Raman spikes in the pump output also for short pulse experiments.

John C. Englund, Charles M. Bowden