Femtosecond filamentation and pulse compression in the wake of molecular alignment

We numerically demonstrate that femtosecond filamentation in a molecular gas can be controlled in the wake of molecular alignment following impulsive rotational Raman excitation with a weak pump pulse. The succeeding filamentation dynamics of the collinearly propagating probe pulse is significantly influenced by the spatiotemporally modulated refractive index at the revivals of molecular alignment. The length of the filament generated by the probe pulse can be efficiently increased to obtain an ultrabroad spectrum and a few-cycle pulse via self-compression by tuning its delay to match the molecular alignment revivals.