Femtosecond filamentation by intensity clamping at a Freeman resonance

TL;DR

This paper reveals that Freeman resonances significantly influence femtosecond filamentation by causing intensity clamping at specific resonances, leading to new filamentation regimes with lower electron densities than traditional models suggest.

Contribution

It demonstrates the impact of Freeman resonances on filamentation dynamics and introduces the concept of filament intensity being clamped at these resonances, challenging existing models.

Findings

Filament peak intensity is clamped at Freeman resonances.

Resonances reduce the transient refractive index.

New filamentation regimes with lower electron densities are identified.

Abstract

We demonstrate that Freeman resonances have a strong impact on the nonlinear optical response in femtosecond filaments. These resonances decrease the transient refractive index within a narrow intensity window and strongly affect the filamentation dynamics. In particular, we demonstrate that the peak intensity of the filament can be clamped at these resonances, hinting at the existence of new regimes of filamentation with electron densities considerably lower than predicted by the standard model. This sheds a new light on the phenomenon of filamentary intensity clamping and the plasmaless filaments predicted by the controversial higher-order Kerr model.