Time domain effects during spontaneous self-channelling of light in air below the collapse threshold

We have studied the temporal effects on ultra-short pulses during their propagation in air below the collapse threshold where spontaneous self-channelling is observed. A rich dynamics in the spatio-temporal properties of the pulse has been obtained both in the theory and experiment. We have shown that different parts of the pulse do not have the same temporal properties because they do not propagate in the same way. Experimental measurements confirm the dependence of the temporal pulse width with the propagation as well as with the transversal coordinate predicted by the theoretical calculations. In particular, this study has lead us to identify the conditions for which an important reduction of the temporal width as well as a clear pedestal cleaning can be achieved