Monte Carlo calculation of ion, electron, and photon spectra of xenon atoms in x-ray free-electron laser pulses

TL;DR

This paper uses Monte Carlo simulations to analyze the ionization, electron, and photon spectra of xenon atoms subjected to XFEL pulses at 4500 eV, revealing complex multiphoton ionization up to charge state +44.

Contribution

It introduces a Monte Carlo approach to efficiently model ionization dynamics of heavy atoms like xenon under XFEL irradiation, overcoming computational challenges of rate equations.

Findings

Xenon can reach charge states up to +44 under XFEL pulses.

Charge state distributions and spectra are characterized at various fluences.

Multiphoton absorption leads to sequential ionization processes.

Abstract

When atoms and molecules are irradiated by an x-ray free-electron laser (XFEL), they are highly ionized via a sequence of one-photon ionization and relaxation processes. To describe the ionization dynamics during XFEL pulses, a rate equation model has been employed. Even though this model is straightforward for the case of light atoms, it generates a huge number of coupled rate equations for heavy atoms like xenon, which are not trivial to solve directly. Here, we employ the Monte Carlo method to address this problem and we investigate ionization dynamics of xenon atoms induced by XFEL pulses at a photon energy of 4500 eV. Charge state distributions, photo-/Auger electron spectra, and fluorescence spectra are presented for x-ray fluences of up to $10^{13}$ photons/$\mu$m$^2$. With the photon energy of 4500 eV, xenon atoms can be ionized up to +44 through multiphoton absorption characterized by sequential one-photon single-electron interactions.