Probing the roto-vibrational dynamics occurring in the wake of optical filamentation

In this work we investigate the roto-vibrational excitation of a molecular medium induced by filamentation of an ultrashort laser pulse. The experiment has been performed using an amplified Ti:sapphire laser system, which generates 60-fs pulses at 800 nm with a repetition rate of 10 Hz. The laser pulses were compressed down to 10 fs by filamentation in an Ar-filled gas cell, followed by reflections on chirped mirrors. The output pulses, with an energy of 1 mJ, were sent to an interferometer; the two time-delayed replicas of the input pulses were collinearly focused into a second cell filled with the gaseous sample. The first (pump) pulse was used to generate a filament, inducing a roto-vibrational excitation in the molecular sample. The second pulse was used to probe the effects occurring in the filament wake. The central part of the two beams was sent to a spectrometer, in order to record the UV tail of the spectrum as a function of the pump-probe delay.