Spectral dependence of purely-Kerr-driven filamentation in air and argon

Abstract

Based on numerical simulations, we show that higher-order nonlinear indices (up to n8 and n10, respectively) of air and argon have a dominant contribution to both focusing and defocusing in the self-guiding of ultrashort laser pulses over most of the spectrum. Plasma generation and filamentation are therefore decoupled. As a consequence, ultraviolet wavelength may not be the optimal wavelength for applications requiring to maximize ionization

Highly extended high density filaments in tight focusing geometry in water: from femtoseconds to microseconds

“…Thus, the filament must collapse, but it does not. Thereby, it could be assumed that a high-order Kerr effect can counterbalance the strong self-focusing, especially at such high laser intensities [36][37][38][39]. The shock wave energy is the square root to its radius due to mass flow conservation and its spherical symmetry [7].…”

1-J white-light continuum from 100-TW laser pulses

“…[18]. In the second regime, we simulated a filamenting beam in a 2D + 1 (propagation distance, radial distance, and time) propagation model based on the nonlinear Schrödinger equation as detailed in [7].…”

“…The plasma generated at the nonlinear focus is generally considered as the main process in that regard, although we recently suggested that the higher-order Kerr effect could play this role [6], in particular for longer wavelengths [7] and/or shorter pulses [8]. Filamentation is now well characterized from the mJ, GW level to the sub-J, TW levels, with potential major atmospheric applications such as lightning triggering and control or laser-induced condensation [9,10].…”

From higher-order Kerr nonlinearities to quantitative modeling of third and fifth harmonic generation in argon

“…In a recent experiment, we have shown that the electronic optical Kerr effect in Ar, N 2 , O 2 , and air exhibits a highly nonlinear behavior versus the applied intensity [1], resulting in a saturation of the nonlinear refractive index observed at moderate intensity, followed by a sign inversion at higher laser intensity. This observation has a substantial impact on the propagation of ultrashort and ultra-intense laser pulses, especially in the context of laser filamentation [2][3][4][5] where the higher-order Kerr effect (HOKE), rather than the defocusing contribution of the free electrons, can play a key role in the self-guiding process [6], especially at long wavelengths [7] and for short pulses [8]. However, this issue is still controversial [9][10][11].…”

“…This equation provides a direct relationship between the power ratio of the harmonics and the ratio of the corresponding non-linear susceptibilities. The latter are related to the nonlinear refractive indices through the relation [7] so that…”