Far-field spectral characterization of conical emission and   filamentation in Kerr media
  By use of an imaging spectrometer we map the far-field ($\theta-\lambda$) spectra of 200 fs optical pulses that have undergone beam collapse and filamentation in a Kerr medium. By studying the evolution of the spectra with increasing input power and using a model based on stationary linear asymptotic wave modes, we are able to trace a consistent model of optical beam collapse high-lighting the interplay between conical emission, multiple pulse splitting and other effects such as spatial chirp. 
Daniele Faccio, Paolo Di Trapani, Stefano Minardi, Alberto Bramati,   Francesca Bragheri, Carlo Liberale, Vittorio Degiorgio...