Spatiotemporal evolution of femtosecond laser pulses guided in air-clad fused-silica nanoweb.

We investigate nonlinear propagation and self-focusing of femtosecond Ti:sapphire laser pulses in an 800-nm-thick silica nanoweb fiber. Different dispersion regimes are accessible by launching TE- or TM-polarized light. Excitation in the anomalous dispersion regime (TM) results in pulse splitting and spectral broadening, which lead to supercontinuum generation, whereas, for normal dispersion (TE, excited close to a zero dispersion wavelength), self-phase modulation causes spectral broadening, which leads at higher power to beam collapse and the creation of a damage track.