Self-steepening is an abrupt process

We discover that self-steepening occurs so fast with slight change in the input energy that it could be considered as an on-off process whose potential application could be far reaching. This observation was carried out by generating a stable uniform pattern of femtosecond filaments inside a methanol cell and measuring the evolution of the white light spectra. We found that the white light supercontinuum, a consequence of self-steepening, turned on almost instantaneously with respect to a very slight change in the energy.