Higher Order Kerr Terms vs. Plasma: Saturation of the Nonlinear Refractive Index
Résumé
In this talk, I will present a study on atomic nonlinear polarization induced by high-intensity ultrashort laser pulses in hydrogen by numerically solving the time-dependent Schrodinger equation. The aim is to reveal the origin of the nonlinear index saturation and subsequent intensity clamping in femtosecond _laments. This allows for the comparison between the proposed model of the higher-order Kerr effect (HOKE) and two versions of the standard model for femtosecond _lamentation, including either a multiphoton or tunnel ionization rate. We find that around the clamping intensity the instantaneous HOKE model does not reproduce the temporal structure of the nonlinear response obtained from the quantum-mechanical results.
In contrast, the noninstantaneous charge contributions included in the standard models ensure a reasonable quantitative agreement. Therefore, the physical origin for the observed saturation of the overall electron response is confirmed to mainly result from contributions of free or nearly-free electrons.