Abstract
During the inaugural experiment at FLASH, the first vacuum ultraviolet (VUV) free-electron laser facility, Wabnitz et al. [Nature 420, 482 (2002)] irradiated xenon clusters and sparked a concerted theoretical and experimental effort to understand how dense, finite plasmas behave under intense irradiation. In this work, we revisit this experiment with a model that is based only on well-established atomic processes. We find that the experimental results can be explained by hybrid quantum-classical molecular-dynamics simulations if collisional excitation, recombination, and a sufficiently deep soft-core potential is used. Our recent theoretical model for inverse bremsstrahlung heating (IBH) is used to show that the measured energy absorbed by the cluster in the experiment is well predicted by our model.
Highlights
In 2001, FLASH, at DESY, began a new era of exploration into vacuum ultraviolet (VUV) light-matter interactions in the nonlinear regime [1,2]
During the inaugural experiment at FLASH, the first vacuum ultraviolet (VUV) free-electron laser facility, Wabnitz et al [Nature 420, 482 (2002)] irradiated xenon clusters and sparked a concerted theoretical and experimental effort to understand how dense, finite plasmas behave under intense irradiation
The first experiment investigated the interaction of xenon clusters with a pulse of sufficiently small wavelength (λ ≈ 100 nm) to allow for single-photon ionization of xenon atoms, and with sufficient intensity to allow for inverse bremsstrahlung heating (IBH) [1]
Summary
In 2001, FLASH, at DESY, began a new era of exploration into vacuum ultraviolet (VUV) light-matter interactions in the nonlinear regime [1,2]. The self-consistent potentials and MBR mechanisms increase the amount of energy absorbed by the cluster, increasing the electron plasma temperature and driving additional collisional ionization. In 2009, Ziaja et al combined these models and followed the energetics of the system by using a nonequilibrium Boltzmann solver with the updated experimental pulse duration and intensity [17] One of their main findings was the strong role recombination played in lowering the charge states of the ions in the core of the cluster. We revisit the intense VUV–xenon-cluster experiment using a model that only relies on well-accepted atomic processes and find that this is sufficient to explain the experimental results, even with the updated pulse parameters. A full picture of both the energetics and ionization of the Wabnitz experiment is presented showing that the energy absorbtion is dominated by IBH and ionization is dominated by collisional processes without the need for additional ionization mechanisms, nor the need for non-Coulombic potentials
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