Stimulated Raman scattering in a pumping field with phase modulated by a Markov process

Yu. S. Oseledchik

A. T. Georges

Yu. P. Malakyan

A theory is developed for transient hyper-Raman scattering and four-wave parametric processes in a gaseous medium subjected to an ultrashort pump pulse field. Investigations are made of the intensity and spectrum of the infrared and ultraviolet radiation generated in a medium as a result of these processes, bearing in mind the transient properties of the pump (phase modulation, pulse profile). It is shown that the initial nonlinearity of the pump field and the parametric processes result in new effects not observed in transient stimulated Raman scattering. For a large two-photon detuning, the hyper-Raman forward scattering is suppressed because of destructive interference with stimulated parametric generation of ultraviolet radiation. The gain of the infrared and ultraviolet radiation depends on the pump pulse profile. Under exact two-photon resonance conditions in the absence of any phase modulation of the pump, infrared and ultraviolet pulses are coherently split into various subpulses and a time-dependent Autler–Townes doublet is observed in their spectrum.

Alexander E. Kozhekin, E. Strelchenko

Yuichiro Kida, Shin-ichi Zaitsu, Totaro Imasaka

Transient stimulated rotational Raman scattering induced by a polarization-modulated femtosecond pulse whose polarization varies with time is reported. The peak intensity of the polarization-modulated pulse produced in this study is low compared to that of a pulse without polarization variation, and this leads to the low efficiency of self-phase-modulation and thus the high efficiency of stimulated Raman scattering compared to the case of a pump pulse without polarization modulation. The scattering process is unique in terms of the high peak ratio of the anti-Stokes to Stokes emissions compared to the ratio in the case of the scattering induced by linearly, circularly, and elliptically polarized pump pulses. Under optimum conditions, the ratio approaches 1, which is not realized in the general case of stimulated rotational Raman scattering.

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/.