2-QUANTUM RAMAN PROCESSES IN ULTRABROADENING OF POWERFUL ULTRASHORT LIGHT-PULSES

The evolution of the spectrum of a powerful electro-magnetic pulse in coherent two-quantum interaction of the Raman type is considered, when the approximation of slowly varying amplitudes for the field and the medium polarization is invalid. It is shown that there exist power thresholds, at which strong self-broadening of the field spectrum occurs, provided frequencies OMEGA (HBAROMEGA = E2 - E1 is the difference of the energies of the levels participating in SRS) are inside the field spectrum. The results obtained agree with the experiments on generation of super-continuum in various media, in particular, self-frequency shift of optical solitons in fibers.