Experimental Tests of the New Paradigm for Laser Filamentation in Gases

TL;DR

This paper tests the traditional understanding of laser filamentation in gases, confirming the established paradigm through electrical and optical measurements, and challenges the recent theory proposing Kerr effect saturation as the main mechanism.

Contribution

The study provides experimental evidence supporting the established paradigm over the new theory suggesting Kerr effect sign reversal dominates filament propagation.

Findings

Results support the traditional Kerr self-focusing and plasma defocusing balance.

Electrical and optical measurements align with the established filamentation model.

The new theory of Kerr saturation is not supported by the experimental data.

Abstract

Since their discovery in the mid-1990s, ultrafast laser filaments in gases have been described as products of a dynamic balance between Kerr self-focusing and defocusing by free electric charges that are generated via multi-photon ionization on the beam axis. This established paradigm has been recently challenged by a suggestion that the Kerr effect saturates and even changes sign at high intensity of light, and that this sign reversal, not free-charge defocusing, is the dominant mechanism responsible for the extended propagation of laser filaments. We report qualitative tests of the new theory based on electrical and optical measurements of plasma density in femtosecond laser filaments in air and argon. Our results consistently support the established paradigm.