Comment on "Saturation of the All-Optical Kerr Effect"

TL;DR

This paper critiques a recent calculation of higher-order Kerr effect coefficients, arguing that their observed saturation and negative nonlinear index are artifacts resulting from inappropriate perturbative ionization theory at high intensities.

Contribution

The authors demonstrate that the previous results are artifacts caused by the breakdown of perturbative ionization theory in high-intensity regimes.

Findings

The negative nonlinear index is an artifact of the perturbative approach.

High-intensity regimes require non-perturbative models for accurate Kerr effect analysis.

The original saturation observed is not physically real, but a modeling artifact.

Abstract

Br\'ee, Demircan, and Steinmeyer [Phys. Rev. Lett. 106, 183902 (2011)] recently calculated higher-order Kerr effect (HOKE) coefficients using the nonlinear Kramers-Kronig relations. We show that the saturated and negative nonlinear index of refraction obtained by Br\'ee et al. is an artifact of their use of a perturbative theory of ionization in an intensity region where it breaks down.