Hidden Charge States in Soft-X-Ray Laser-Produced Nanoplasmas Revealed by Fluorescence Spectroscopy

Abstract

Highly charged ions are formed in the center of composite clusters by strong free-electron laser pulses and they emit fluorescence on a femtosecond time scale before competing recombination leads to neutralization of the nanoplasma core. In contrast to mass spectrometry that detects remnants of the interaction, fluorescence in the extreme ultraviolet spectral range provides fingerprints of transient states of high energy density matter. Spectra from clusters consisting of a xenon core and a surrounding argon shell show that a small fraction of the fluorescence signal comes from multiply charged xenon ions in the cluster core. Initially, these ions are as highly charged as the ions in the outer shells of pure xenon clusters with charge states up to at least 11+.

Correlated electronic decay in expanding clusters triggered by intense XUV pulses from a Free-Electron-Laser

“…The Ar + charge state dominates in Xe-Ar cluster spectra, similar to a previous work on Xe-Ar mixed clusters33. Even though the absorption cross-section of Xe in this photon energy range is much higher (24.7 Mb compared to 1.4 Mb for Ar46), the ratio of Xe to Ar atoms in clusters is about one to ten323334. Therefore, the large fraction of Ar + ions is indicative for a more efficient electron-ion recombination inside the Xe core as compared to the Ar shell3345.…”

“…Smaller and larger Xe core - Ar shell clusters of 〈 Ν 〉 = 400 and 4000 atoms were prepared by expanding the gas premix at 7 and 17 bars, respectively. According to previous studies323334 the estimated Xe enrichment factor was around 10. This resulted in the core-shell structures roughly consisting of 80 and 800 Xe atoms in the core with 1–2 and 3–4 Ar layers on top of it, respectively.…”

“…The core-shell structures consist of a Xe core covered by 3–4 and 1–2 layers of Ar for larger and smaller clusters, respectively323334. All spectra were measured after irradiation of the target with XUV pulses with a photon energy of 92 eV and an estimated average intensity in the interaction region of 2 × 10 15  W/cm 2 .…”

Electron and fluorescence spectra of a water molecule irradiated by an x-ray free-electron laser pulse

“…The capability of XFELs to provide ultrashort pulses has enabled novel time-resolved spectroscopic experiments [11][12][13][14]. The work presented here is connected to the ultrahigh intensity of XFELs that has rendered a new regime in nonlinear x-ray spectroscopy accessible [15][16][17][18][19].…”

A validation of a simple model for the calculation of the ionization energies in X-ray laser-cluster interactions

“…16 The LIT model also leads to a precise definition for the inner-ionization threshold, an integral part of quantumclassical hybrid models of laser-cluster interactions which seek to describe the microscopic, time-dependent interaction of ultra-intense lasers with clusters. An accurate model of ionization will, thus, significantly improve the confidence in the transient properties of the laser-cluster interaction, which are now being probed experimentally, [25][26][27] and not just the final products. In this work, the LIT model is compared with detailed coupled cluster quantum calculations on small systems of atoms and ions to mimic cluster conditions at the most approximate stage of the calculation, the initial state when the ions are closest together.…”