Evolution of the ionic polarization in multiple sequential ionization: general equations and an illustrative example

TL;DR

This paper develops comprehensive rate equations incorporating radiation polarization to model sequential ionization, demonstrated through krypton ionization by intense femtosecond EUV pulses, revealing polarization's impact on ion yields and spectra.

Contribution

It introduces a complete polarization-aware rate equation framework for sequential ionization processes, extending previous models that neglected polarization effects.

Findings

Ion yields depend on radiation polarization and photon fluence.

Polarization significantly influences photoelectron spectra.

Theoretical results match expected polarization-dependent ionization behaviors.

Abstract

The modern Free-Electron-Lasers generate a highly intense polarized radiation which initiate a sequence of ionization and decay events. Their probability depends on the polarization of each state as function of time. Its complete accounting is limited by the fact that a state can be formed in various ways. Here we present the equivalent of rate equations for population that completely accounts polarization of radiation and formulated in terms of the statistical tensors. To illustrate our approach we theoretically consider sequential photoionization of krypton by an intense extreme ultraviolet femtosecond pulse for the photon energies below the 3d-shell excitation threshold. The calculations of the ion yields, photoelectron spectra and ionic polarization for various photon fluence are presented and role of polarization is discussed.