Self-guiding of femtosecond light pulses in condensed media: Plasma generation versus chromatic dispersion

We investigate the nonlinear self-guiding of ultrashort laser pulses in dielectric solids, such as fused silica. Emphasis is given to the role of chromatic dispersion compared with plasma generation. A basic set of propagation equations is derived analytically and provides a nonlinear Schrödinger model accounting for high-order dispersion, space–time focusing, self-steepening and plasma generation. Three typical propagation regimes at the laser wavelengths of 790 nm, 1550 nm and 1275 nm, respectively promoting normal, anomalous and near-zero group velocity dispersions (GVD), are examined by means of theoretical arguments and numerical simulations. It is shown that normal GVD may favor a significant self-guiding with inessential plasma generation, which does not occur in anomalous GVD regimes. Spectral broadening at these three laser wavelengths is commented on, in the light of the temporal distortions undergone by the pulses.