High-field quantum calculation reveals time-dependent negative Kerr contribution

TL;DR

This paper uses quantum simulations to reveal a significant, previously overlooked negative Kerr effect in hydrogen under strong infrared laser fields, explaining recent experimental observations of higher-order nonlinearities.

Contribution

It introduces a full quantum time-dependent model that uncovers a quasi-instantaneous negative Kerr contribution absent in traditional weak-field models.

Findings

Identification of a negative Kerr contribution in hydrogen under strong fields

Explanation of higher-order Kerr effects observed experimentally

Demonstration of the importance of electron-ion interactions in nonlinear response

Abstract

The exact quantum time-dependent optical response of hydrogen under strong field near infrared excitation is investigated and compared to the perturbative model widely used for describing the effective atomic polarization induced by intense laser fields. By solving the full 3D time-dependent Schr\"{o}dinger equation, we exhibit a supplementary, quasi-instantaneous defocusing contribution missing in the weak-field model of polarization. We show that this effect is far from being negligible in particular when closures of ionization channels occur and stems from the interaction of electrons with their parent ions. It provides an interpretation to higher-order Kerr effect recently observed in various gases.