Perturbative theory of ensemble-averaged atomic dynamics in fluctuating laser fields

TL;DR

This paper introduces a perturbative approach using multitime cumulants to model atomic ionization in fluctuating laser fields, accounting for field coherence and intensity effects, validated against Monte-Carlo simulations.

Contribution

The paper presents a novel perturbative method based on multitime cumulants for modeling atomic dynamics in fluctuating laser fields, incorporating field coherence properties.

Findings

Ionization lineshape becomes Voight profile influenced by field coherence.

Model's validity depends on field coherence time and intensity.

Results align with Monte-Carlo calculations for specific conditions.

Abstract

We have developed a perturbative method to model the resonant ionization of atomic systems in fluctuating laser fields. The perturbative method is based on an expansion in terms of the multitime cumulants, a suitable combination of moments (field's coherence functions), used to represent the field's statistical properties. The second-order truncated expansion is expressed in terms of the radiation's power spectrum and the intensity autocorrelation function. We investigate the range of validity of the model in terms of the field's coherence temporal length and peak intensity and have compared the results with conventional Monte-Carlo calculations. We apply the theory in the case of a near-resonant ionization of the Helium 2s2p autoionizing state with a SASE FEL pulse with square-exponentially dependent 1st-order coherence function. The ionization lineshape profile acquires a Voight profile; the degree of the Gaussian or Lorentzian character of which to depend crucially on the field's coherence time.