Enhanced One-Color-Two-Photon Resonant Ionization in Highly Charged Ions by Fine-Structure Effects
Authors
Moto Togawa
Chunhai Lyu
Chintan Shah
Marc Botz
Joschka Goes
Jonas Danisch
Marleen Maxton
Kai Köbnick
Filipe Grilo
Pedro Amaro
Katharina Kubicek
Mohammed Sekkal
Awad Mohamed
Rebecca Boll
Alberto De Fanis
Simon Dold
Tommaso Mazza
Jacobo Montano
Nils Rennhack
Björn Senfftleben
Sergey Usenko
Zoltan Harman
Christoph H. Keitel
Maurice Leutenegger
Michael Meyer
Thomas Pfeifer
José R. Crespo López-Urrutia
Thomas M. Baumann
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.
