Spatio-temporal reshaping and X wave dynamics in optical filaments

We investigate ultrashort laser pulse filamentation within
the framework of spontaneous X Wave formation. After a brief overview
of the filamentation process we study the case of an intense filament
co-propagating with a weaker seed pulse. The filament is shown to induce
strong Cross-Phase-Modulation (XPM) effects on the weak seed pulse:
driven by the pump, the seed pulse undergoes pulse splitting with the
daughter pulses slaved to their pump counterparts. They undergo strong
spatio-temporal reshaping and are transformed into XWaves traveling at the
same group velocities as the pump split-off pulses. In the presence of a gain
mechanism such as Four-Wave-Mixing or Stimulated Raman Scattering,
energy is then transferred from the pump filament leading to amplification
of the seed X Wave and formation of a temporally compressed intensity
peak.