On the Saturation of the Nonlinear Refractive Index in Atomic Gases

Abstract

Motivated by the ongoing controversy on the origin of the nonlinear index saturation and subsequent intensity clamping in femtosecond filaments, we study the atomic nonlinear polarization induced by a high-intensity and ultrashort laser pulse in hydrogen by numerically solving the time dependent Schrödinger equation. Special emphasis is given to the efficient modeling of the nonlinear polarization at central laser frequency corresponding to 800 nm wavelength. Here, the recently proposed model of the Higher-Order Kerr Effect (HOKE) and two versions of the Standard model for femtosecond filamentation, including either a multi-photon or tunnel ionization rate, are compared. 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 non-instantaneous 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.

9 pages, 5 figures

References in corpus (4)

• Ultrashort filaments of light in weakly-ionized, optically-transparent media
• Higher-order Kerr terms allow ionization-free filamentation in gases
• Transition from plasma- to Kerr-driven laser filamentation
• High-field quantum calculation reveals time-dependent negative Kerr contribution

Cited by in corpus (8)

• Bound electron nonlinearity beyond the ionization threshold
• Terahertz generation in dual-color laser: continuum electron in strong-field single-atom ionization
• Saturable Lorentz model for fully explicit three-dimensional modeling of nonlinear optics
• On the interpretation of negative birefringence observed in strong-field optical pump-probe experiments: high-order Kerr and plasma grating effects
• Adiabatic Floquet model for the optical response in femtosecond filaments
• Ab-initio calculations of laser-atom interactions reveal harmonics feedback during macroscopic propagation
• Modulational instability windows in the nonlinear Schrödinger equation involving higher-order Kerr responses
• Nonlinear Nonperturbative Optics Model Enriched by Evolution Equation for Polarization