Infrared extension of femtosecond supercontinuum generated by filamentation in solid-state media

We carried out experimental and numerical study of the ultrafast supercontinuum generation by filamentation of 120 fs, 800 nm laser pulses in sapphire under variable focusing conditions. We demonstrate that the supercontinuum spectra produced in loose focusing conditions have much larger infrared extent, while the spectral blueshift remains fairly the same. Our numerical simulations reproduce the experimental results in great detail and disclose that the input beam focusing conditions affect only the nonlinear propagation of the leading sub-pulse, which emerges after the pulse splitting event, and which is responsible for the redshifted spectral broadening.