Intense VUV laser cluster interaction in the strong coupling regime

Jungreuthmayer, Christian; Ramunno, Lora; Zanghellini, Jürgen; Brabec, Thomas

doi:10.1088/0953-4075/38/16/013

Cited by 97 publications

(107 citation statements)

References 20 publications

(21 reference statements)

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“…As suggested in ref. [22], this small discrepancy between experiment and our predictions may be due to the fact that at low fluences the many-body recombination effects within the cold electron plasma can be important [20]. They could then lead to higher ionization states that we do not observe within this model.…”

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confidence: 71%

“…Several interesting theoretical models have been proposed in order to describe the evolution of clusters exposed to intense VUV pulses [15,16,17,18,19,20,21]. The most explored ones are: i) heating of quasi-free electrons due to enhanced inverse bremsstrahlung (IB) [15,16], ii) enhanced photoionization within the sample due to lowering of interatomic potential barriers [17,18], and iii) heating due to manybody recombination processes [20]. Each of these various approaches lead to the significantly enhanced energy absorption in agreement with the experimental data [11].…”

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confidence: 99%

“…The total ionization rate within the sample was affected most by the inverse bremsstrahlung heating rate applied. Within the theoretical framework defined above we estimated that: i) many-body effects (many-body recombination) [20] could contribute only for clusters irradiated at low pulse fluences, ii) the plasma environment effects estimated with electron screened atomic potentials were small. This was in contrast to the estimates of Ref.…”

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Energetics, Ionization, and Expansion Dynamics of Atomic Clusters Irradiated with Short Intense Vacuum-Ultraviolet Pulses

et al. 2009

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Kinetic Boltzmann equations are used to model the ionization and expansion dynamics of xenon clusters irradiated with short intense VUV pulses. This unified model includes predominant interactions that contribute to the cluster dynamics induced by this radiation. The dependence of the evolution dynamics on cluster size, Natoms = 20 − 90000, and pulse fluence, F = 0.05 − 1.5 J/cm 2 , corresponding to intensities in the range, 10 12 − 10 14 W/cm 2 and irradiation times, ≤ 50 fs, is investigated. The predictions obtained with our model are found to be in good agreement with the experimental data. We find that during the exposure the cluster forms a shell structure consisting of a positively charged outer shell and a core of net charge equal to zero. The width of these shells depends on the cluster size. The charged outer shell is large within small clusters (Natoms = 20, 70), and its Coulomb explosion drives the expansion of these clusters. Within the large clusters (Natoms = 2500, 90000) the neutral core is large, and after the Coulomb explosion of the outer shell it expands hydrodynamically. Highly charged ions within the core recombine efficiently with electrons. As a result, we observe a large fraction of neutral atoms created within the core, its magnitude depending on the cluster size. Atomic clusters are excellent objects to test the dynamics within samples irradiated with radiation from short wavelength free-electron-lasers (FELs) [1,2,3]. Their physical properties put them on the border between the solid state and the gas phase. Cluster studies are important for planned experiments with FELs in solid state physics, materials science and for studies of the extreme states of matter [4]. Accurate predictions on the ionization, thermalization and expansion timescales within irradiated samples that can be obtained with cluster experiments are also needed for exploring the limits of experiments on single particle diffraction imaging [5,6,7,8,9,10].During the first cluster experiments performed at the free-electron-laser facility FLASH at DESY with VUV photons of energy, E = 12.7 eV, and power densities up to a few 10 13 W/cm 2 [11] highly charged Xe ions (up to +8) of high kinetic energies were detected. This unexpectedly strong energy absorption could not be explained using the standard approaches [12,13,14]. More specifically, the energy absorbed was almost an order of magnitude larger than that predicted with classical absorption models, and the ion charge states created were much higher than those observed during the irradiation of * Corresponding author. E-mail: ziaja@mail.desy.de isolated atoms in similar conditions. This indicated that at such radiation wavelengths some processes specific to many-body systems were responsible for an enhanced energy absorption.The physics underlying the dynamics within the irradiated clusters is complex. Several interesting theoretical models have been proposed in order to describe the evolution of clusters exposed to intense VUV pulses [15,16,17,18,19,20,21]. The most exp...

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confidence: 99%

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Energetics, Ionization, and Expansion Dynamics of Atomic Clusters Irradiated with Short Intense Vacuum-Ultraviolet Pulses

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“…These surprising results stimulated intense theoretical effort. Several interesting models have been proposed [Santra & Greene, 2003, Siedschlag & Rost, 2004, Bauer, 2004, Jungreuthmayer et al, 2005, which could explain various aspects of the increased photoabsorption and ionization dynamics observed in the experiments (for review see [Saalmann et al, 2006]). On the other hand, there are still some controversies, e. g. regarding the role of the inverse bremsstrahlung mechanism, screening effects and of the inner ionization processes in the ionization dynamics.…”

Section: Introductionmentioning

confidence: 99%

Statistical model of radiation damage within an atomic cluster irradiated by photons from free-electron-laser

Ziaja¹,

Weckert²,

Möller

2007

Laser Part. Beams

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Abstract:Here we report on the present status of our project on statistical modelling of charge dynamics within irradiated samples. Boltzmann statistical approach to model the radiation damage in samples irradiated by FEL photons is tested in a study case of a spherically symmetric xenon cluster. Qualitative agreement between the model predictions and the experimental data is found. The results obtained demonstrate the potential of the statistical method for describing the non-equilibrium dynamics of samples exposed to FEL radiation.

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“…Because the ponderomotive energy scales with ω −2 (ω-laser frequency) and thus, the direct effect of the laser field on the electron movement is small, it was a big surprise when experiments in the vacuum-ultraviolet spectral regime at 100 nm and intensities up to 10 13 W cm −2 reported unexpectedly high-energy absorption and complete Coulomb explosion of clusters [8]. The efficient energy absorption of the clusters is theoretically explained with more realistic potentials for IBS [9], barrier suppression in the ionized cluster [10] and enhanced heating through many-body collisions in a transient strongly coupled nanoplasma [11]. While theoretically IBS is predicted to be the dominant absorption mechanism down to 62 nm [12] recent photoemission experiments at λ = 32 nm and similar intensities find no evidence for it [13].…”

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confidence: 99%

Charge recombination in soft x-ray laser produced nanoplasmas

Hoener¹,

Thomas²,

Wabnitz³

et al. 2009

J. Phys.: Conf. Ser.

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The ionization and charge separation processes of nanoplasmas created by resonant excitation of atomic clusters in intense soft x-ray pulses have been investigated. Through irradiation with femtosecond pulses from the FLASH free electron laser (FEL) at λ = 13.7 nm and power densities exceeding 10 14 W cm −2 the clusters are highly ionized with transient atomic charge states up to 9+. Variation of the cluster composition from pristine to doped and core-shell systems allows tracking of the spatial origin and charge states of the fragments yielding insight into the nanoplasma dynamics. The data give evidence for efficient charge redistribution processes leading to a Coulomb explosion of the cluster outer part and recombination of the nanoplasma core. The experiments show qualitatively different processes for (soft) x-ray produced nanoplasmas from the optical (IR) strong-field regime where the clusters disintegrate completely in a Coulomb explosion.(Some figures in this article are in colour only in the electronic version)Understanding the interaction of light with matter has been a central theme of physics over the past century, starting with the concept of the photon and the inception of quantum theory. The invention of the laser and the continuing advance in laser technologies has made it possible to explore regimes of nonlinear light-matter interaction leading to novel laserbased concepts for particle accelerators, plasma formation and nuclear fusion [1]. Currently, we are witnessing the advent of intense lasers in the x-ray regime. One of the most exciting prospects of research with x-ray lasers is direct imaging of nonperiodic nanoscale objects, such as biomolecules, nanocrystals, living cells and viruses [2]. Even though it is crucial for the success of the imaging experiments, understanding the interaction of intense x-ray pulses with atomic systems and the underlying dynamics is still in its infancy. To date, virtually all studies about the ionization as well as nuclear dynamics of nanometer-sized structures in intense (soft) x-ray pulses are of theoretical nature [3][4][5][6] and no experimental data are available.For the experimental investigations of matter in intense light pulses atomic clusters are ideal because their size can be tuned from the molecular to the bulk-like regime and there is no energy dissipation into surrounding media. The ionization dynamics of clusters in intense laser pulses depend considerably on the radiation wavelength. In the infrared spectral regime the cluster is ionized by the optical field and the resulting transient nanoplasma is efficiently heated by the external laser field via inverse bremsstrahlung (IBS) and collective effects, leading to a Coulomb explosion of the cluster [7]. Because the ponderomotive energy scales with ω −2 (ω-laser frequency) and thus, the direct effect of the laser field on the electron movement is small, it was a big surprise when experiments in the vacuum-ultraviolet spectral regime at 100 nm and intensities up to 10 13 W cm −2 reported u...

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Intense VUV laser cluster interaction in the strong coupling regime

Cited by 97 publications

References 20 publications

Energetics, Ionization, and Expansion Dynamics of Atomic Clusters Irradiated with Short Intense Vacuum-Ultraviolet Pulses

Energetics, Ionization, and Expansion Dynamics of Atomic Clusters Irradiated with Short Intense Vacuum-Ultraviolet Pulses

Statistical model of radiation damage within an atomic cluster irradiated by photons from free-electron-laser

Charge recombination in soft x-ray laser produced nanoplasmas

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