A1 Refereed original research article in a scientific journal
Resonance-Enhanced Multiphoton Ionization in the X-Ray Regime
Authors: LaForge Aaron C., Son Sang-Kil, Mishra Debadarshini, Ilchen Markus, Duncanson Stephen, Eronen Eemeli, Kukk Edwin, Wirok-Stoletow Stanislaw, Kolbasova Daria, Walter Peter, Boll Rebecca, De Fanis Alberto, Meyer Michael, Ovcharenko Yevheniy, Rivas Daniel E., Schmidt Philipp, Usenko Sergey, Santra Robin, Berrah Nora
Publisher: AMER PHYSICAL SOC
Publication year: 2021
Journal: Physical Review Letters
Journal name in source: PHYSICAL REVIEW LETTERS
Journal acronym: PHYS REV LETT
Article number: ARTN 213202
Volume: 127
Issue: 21
Number of pages: 7
ISSN: 0031-9007
eISSN: 1079-7114
DOI: https://doi.org/10.1103/PhysRevLett.127.213202
Self-archived copy’s web address: https://arxiv.org/abs/2110.08145
Here, we report on the nonlinear ionization of argon atoms in the short wavelength regime using ultraintense x rays from the European XFEL. After sequential multiphoton ionization, high charge states are obtained. For photon energies that are insufficient to directly ionize a 1s electron, a different mechanism is required to obtain ionization to Ar17+. We propose this occurs through a two-color process where the second harmonic of the FEL pulse resonantly excites the system via a 1s -> 2p transition followed by ionization by the fundamental FEL pulse, which is a type of x-ray resonance-enhanced multiphoton ionization (REMPI). This resonant phenomenon occurs not only for Ar16+, but also through lower charge states, where multiple ionization competes with decay lifetimes, making x-ray REMPI distinctive from conventional REMPI. With the aid of state-of-the-art theoretical calculations, we explain the effects of x-ray REMPI on the relevant ion yields and spectral profile.
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