Xenon clusters in an intense soft-x-ray pulse are examined in detail and compared with recent experimental results by reproducing the experimental signals (Thomas et al 2009 J. Phys. B: At. Mol. Opt. Phys. 42 134018).Good agreement is found between our theoretical model and the experimental results. A detailed analysis of the experimental signals and their constituents is performed. We find that, unlike large clusters, the smaller N = 147 have a saturated electron kinetic energy distribution (Bostedt et al 2010 New J. Phys. 12 083004). We also find the highest charge states which are detected were initially on the outer shell of the cluster whereas the core ions recombine significantly and are detected as only moderately or singly charged (Hoener et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 181001). Further, we find it is the outer shell ions which obtain the highest kinetic energy upon disintegration (Trost et al

The impact of atomic excited states is investigated via a detailed model of laser-cluster interactions, which is applied to rare gas clusters in intense femtosecond pulses in the extreme ultraviolet (XUV). This demonstrates the potential for a two-step ionization process in laser-cluster interactions, with the resulting intermediate excited states allowing for the creation of high charge states and the rapid dissemination of laser pulse energy. The consequences of this excitation mechanism are demonstrated through simulations of recent experiments in argon clusters interacting with XUV radiation, in which this two-step process is shown to play a primary role; this is consistent with our hypothesis that XUV-cluster interactions provide a unique window into the role of excited atomic states due to the relative lack of photoionization and laser field-driven phenomena. Our analysis suggests that atomic excited states may play an important role in interactions of intense radiation with materials in a variety of wavelength regimes, including potential implications for proposed studies of single molecule imaging with intense X-rays.Over the last decade, coherent radiation sources have been developed that can probe light-matter interactions at ever smaller wavelengths and unprecedented intensities [1,2]. Recent experiments have moved into the extreme ultraviolet (XUV), including several that have explored intense XUV interactions with rare gas clusters [3,4]. The XUV regime near 30 nm is unique because the photon energy is too small for inner shell ionization of rare gas atoms, yet too large (at reported intensities) for any appreciable laser field-driven processes that dominate intense laser-cluster interactions at longer wavelengths, such as collisional heating. We therefore propose that this regime presents a unique opportunity to isolate the influence of the internal electronic structure of atoms within clusters on intense radiation-cluster interactions.To date, models of cluster interactions with intense radiation in the near IR [5] or in the vacuum ultraviolet (VUV) [6][7][8][9] have not incorporated the effects of the atomic structure of the constituent atoms. As a result, the influence of the atomic structure in such interactions is unknown over a broad range of wavelengths, including in the XUV.In this Letter, we introduce a general model that explicitly incorporates the effect of atomic and ionic excited states on collisional ionization, and apply it to a molecular dynamics code for rare gas cluster interactions with intense radiation. By including the process whereby a ground-state electron of any charge species can be internally promoted to an excited state by a colliding electron, ionization is allowed to occur through a two-step process: excitation followed by ionization from the excited state. This requires two sequential collisions, each of less energy than is required by single step collisional ionization from the ground state (the conventional model used widely across wavelength regimes). This generall...

We examine the effect of cluster size on the interaction of Ar 55 -Ar 2057 with intense extreme ultraviolet (XUV) pulses, using a model we developed earlier that includes ionization via collisional excitation as an intermediate step. We find that the dynamics of these irradiated clusters is dominated by collisions. Larger clusters are more highly collisional, produce higher charge states, and do so more rapidly than smaller clusters. Higher charge states produced via collisions are found to reduce the overall photon absorption, since charge states of Ar 2+ and higher are no longer photoaccessible. We call this mechanism collisionally reduced photoabsorption, and it decreases the effective cluster photoabsorption cross section by more than 30% for Ar 55 and 45% for Ar 2057 . The time evolution of the electron kinetic energy distribution begins as a (mostly) Maxwellian distribution. Further, the electron velocity distribution of large clusters quickly become isotropic while smaller clusters retain the inherent anisotropy created by photoionization. Last, the total electron kinetic-energy distribution is integrated over the spatial profile of the laser and the log-normal distribution of cluster size for comparison with a recent experiment [C. Bostedt et al., Phys. Rev. Lett. 100, 133401 (2008)], and good agreement is found.

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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.