Filamentation of a phase-modulated pulse under conditions of normal, anomalous and zero group velocity dispersion

We have investigated experimentally and numerically the influence of the initial temporal phase modulation of a pulse on the spatiotemporal intensity distribution and the frequency-angular spectrum of femtosecond laser pulses with self-channelling in a condensed medium. We have detected a decrease in the intensity of divergent anti-Stokes frequency components during filamentation of radiation under conditions of normal group-velocity dispersion (GVD) and strong phase modulation. In the zero-GVD regime under conditions of the phase modulation of radiation, the spatiotemporal transformation of the pulse is similar to that in the normal-GVD regime, which leads to a qualitative change in the supercontinuum spectrum. In the anomalous-GVD regime, a sequence of 'light bullets' is formed in the filament for both a phase-modulated and a transform-limited pulse.