Band-Gap Dependence of the Ultrafast White-Light Continuum

We report an investigation of white-light continuum generation during self-focusing in extended transparent media using 140-fs Ti:sapphire laser pulses. A band-gap threshold is found above which the width of the continuum tends to increase with increasing band gap and below which there is no continuum generation. This is, to our knowledge, the first report of a parameter predicting the width of the continuum in condensed media. Multiphoton excitation of electrons into the conduction band is proposed as the primary mechanism reponsible for the observations.