Enhanced One-Color-Two-Photon Resonant Ionization in Highly Charged Ions by Fine-Structure Effects
Abstract
Ultraintense pulses from X-ray free-electron lasers can drive, within femtoseconds, multiple processes in the inner shells of atoms and molecules in all phases of matter. The ensuing complex ionization pathways of outer-shell electrons from the neutral to the final highly charged states make a comparison with theory enormously difficult. We resolve these pathways by preparing highly charged ions in an electron beam ion trap before exposing them to the pulsed radiation. This reveals how relativistic fine-structure effects shift electronic energies, largely compensate the core-screening potential, and enable the consecutive, resonant absorption of two quasi-monochromatic X-ray photons that would generally be unfeasible. This doubly-resonant channel enhances the efficiency of two-photon ionization by more than two orders of magnitude, dominating in this regime the nonlinear interaction of light and matter with possible application for future precision X-ray metrology.
Keywords
Cite
@article{arxiv.2511.05148,
title = {Enhanced One-Color-Two-Photon Resonant Ionization in Highly Charged Ions by Fine-Structure Effects},
author = {Moto Togawa and Chunhai Lyu and Chintan Shah and Marc Botz and Joschka Goes and Jonas Danisch and Marleen Maxton and Kai Köbnick and Filipe Grilo and Pedro Amaro and Katharina Kubicek and Mohammed Sekkal and Awad Mohamed and Rebecca Boll and Alberto De Fanis and Simon Dold and Tommaso Mazza and Jacobo Montano and Nils Rennhack and Björn Senfftleben and Sergey Usenko and Zoltan Harman and Christoph H. Keitel and Maurice Leutenegger and Michael Meyer and Thomas Pfeifer and José R. Crespo López-Urrutia and Thomas M. Baumann},
journal= {arXiv preprint arXiv:2511.05148},
year = {2025}
}