Time-gated angular-spectrum characterization of fs-beam filamentation in water

We exploited the new gated angular spectrum (GAS) technique for characterising the complex non-linear dynamics of intense fs infrared pulses underlying beam filamentation in water. The measurements allowed us to discover that the axial white-light continuum and the off-axis coloured conical emission (CCE) are generated by different temporal portions of the light filament, the red and blue-shifted continuum being produced at the trailing and leading edge, respectively, while CCE at the pulse center. Finally, by implementing a FROG type data analysis on the GAS scheme, we were able to retrieve the phase profile of the wave-packet too.