Rotational Raman effects in the wake of optical filamentation.

The spatiotemporal effects generated in the wake of a laser filament propagating in nitrogen are investigated. At suitable time delays, a probe light pulse propagating along the wake experiences a strong spatial confinement and a noticeable spectral broadening at the same time. Numerical simulations, well reproducing the experimental findings, show the key role of the impulsive rotational Raman response in the observed phenomena.