Femtosecond laser filamentation is a highly nonlinear propagation mode. When a laser pulse propagates with a peak power exceeding a critical value Pcr (5 GW at 800 nm in air), the Kerr effect tends to collapse the beam until the intensity is high enough to ionize the medium, giving rise to plasma defocusing. A dynamic competition between these two effects takes place leaving a thin and weakly ionized plasma channel in the trail of the pulse. When an ultrafast laser pulse interacts with molecules, it will align them, spinning them about their axis of polarization. As the quantum rotational wave packet relaxes, the molecules will experience periodic field-free alignment. Recent work has demonstrated the effect of molecular alignment on laser filamentation of ultra-short pulses. Revival of the molecular alignment can modify filamentation parameters as it can locally modify the refractive index and the ionization rate. In this thesis, we demonstrate with simulations and experiments that these changes in the filament parameters (collapse distance and filament plasma length) can be used to probe molecular alignment in CO2.