Resonance-Enhanced Multiphoton Ionization in the X-Ray Regime
Abstract
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 1 s 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 1 s →2 p 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.
- Publication:
-
Physical Review Letters
- Pub Date:
- November 2021
- DOI:
- 10.1103/PhysRevLett.127.213202
- arXiv:
- arXiv:2110.08145
- Bibcode:
- 2021PhRvL.127u3202L
- Keywords:
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- Physics - Atomic Physics;
- Physics - Optics
- E-Print:
- 8 pages, 5 figures, one supplementary material (not included)