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Abstract of [LaForge21]

[LaForge21]
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Resonance-enhanced multiphoton ionization in the x-ray regime

Aaron C. LaForge, Sang-Kil Son, Debadarshini Mishra, Markus Ilchen, Stephen Duncanson, Eemeli Eronen, Edwin Kukk, Stanislaw Wirok-Stoletow, Daria Kolbasova, Peter Walter, Rebecca Boll, Alberto De Fanis, Michael Meyer, Yevheniy Ovcharenko, Daniel E. Rivas, Philipp Schmidt, Sergey Usenko, Robin Santra, and Nora Berrah

Phys. Rev. Lett. 127, 213202 (2021)

[bib][BibTeX][pdf][pdf][link]doi:10.1103/PhysRevLett.127.213202

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.

Tags: Ar, resonance, x-ray, REMPI, XREMPI, XATOM, European XFEL, experiment, XFEL, CFEL, DESY


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