313 research outputs found

    Asymmetric emission of high energy electrons in the two-dimensional hydrodynamic expansion of large xenon clusters irradiated by intense laser fields

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    Energy spectra and angular distributions have been measured of electrons that are emitted upon disassembly of Xe150000Xe_{150000} following irradiation by intense (1015−1016^{15}-10^{16} W cm−2^{-2}) laser pulses whose durations are varied over the 100-2200 fs range. The cluster explosion dynamics occur in the hydrodynamic regime. Electron emission is found to be unexpectedly asymmetric and exhibits a resonance when the laser pulse duration is ∼\sim1 ps. These results are rationalized by extending the hydrodynamic model to also take into account the force that the light field exerts on the polarization charge that is induced on surface of the cluster. We show that the magnitude of this electrostrictive force is comparable to those of Coulombic and the hydrodynamic forces, and it exhibits resonance behavior. Contrary to earlier understanding, we find that low-energy electrons are connected to the resonance in energy absorption by the cluster. The high-energy electrons seem to be produced by a mechanism that is not so strongly influenced by the resonance.Comment: 1 Revtex file, 8 figs. in eps forma

    Explosions of water clusters in intense laser fields

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    Energetic, highly-charged oxygen ions, Oq+O^{q+} (q≤6q\leq 6), are copiously produced upon laser field-induced disassembly of highly-charged water clusters, (H2O)n(H_2O)_n and (D2O)n(D_2O)_n, n∼n\sim 60, that are formed by seeding high-pressure helium or argon with water vapor. ArnAr_n clusters (n∼\sim40000) formed under similar experimental conditions are found undergo disassembly in the Coulomb explosion regime, with the energies of Arq+Ar^{q+} ions showing a q2q^2 dependence. Water clusters, which are argued to be considerably smaller in size, should also disassemble in the same regime, but the energies of fragment Oq+^{q+} ions are found to depend linearly on qq which, according to prevailing wisdom, ought to be a signature of hydrodynamic expansion that is expected of much larger clusters. The implication of these observations on our understanding of the two cluster explosion regimes, Coulomb explosion and hydrodynamic expansion, is discussed. Our results indicate that charge state dependences of ion energy do not constitute an unambiguous experimental signature of cluster explosion regime.Comment: Submitted to Phys. Rev.

    Experimental Observation of Resonance Effects in Intensely Irradiated Atomic Clusters

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    We have resolved the expansion of intensely irradiated atomic clusters on a femtosecond time scale. These data show evidence for resonant heating, similar to resonance absorption, in spherical cluster plasmas

    Enhanced ionization in small rare gas clusters

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    A detailed theoretical investigation of rare gas atom clusters under intense short laser pulses reveals that the mechanism of energy absorption is akin to {\it enhanced ionization} first discovered for diatomic molecules. The phenomenon is robust under changes of the atomic element (neon, argon, krypton, xenon), the number of atoms in the cluster (16 to 30 atoms have been studied) and the fluency of the laser pulse. In contrast to molecules it does not dissappear for circular polarization. We develop an analytical model relating the pulse length for maximum ionization to characteristic parameters of the cluster

    Electron release of rare gas atom clusters under an intense laser pulse

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    Calculating the energy absorption of atomic clusters as a function of the laser pulse length TT we find a maximum for a critical T∗T^*. We show that T∗T^* can be linked to an optimal cluster radius R∗R^*. The existence of this radius can be attributed to the enhanced ionization mechanism originally discovered for diatomic molecules. Our findings indicate that enhanced ionization should be operative for a wide class of rare gas clusters. From a simple Coulomb explosion ansatz, we derive an analytical expression relating the maximum energy release to a suitably scaled expansion time which can be expressed with the pulse length T∗T^*.Comment: 4 pages, 5 figure

    Ionization of clusters in strong X-ray laser pulses

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    The effect of intense X-ray laser interaction on argon clusters is studied theoretically with a mixed quantum/classical approach. In comparison to a single atom we find that ionization of the cluster is suppressed, which is in striking contrast to the observed behavior of rare-gas clusters in intense optical laser pulses. We have identified two effects responsible for this phenomenon: A high space charge of the cluster in combination with a small quiver amplitude and delocalization of electrons in the cluster. We elucidate their impact for different field strengths and cluster sizes.Comment: 4 pages, 4 figure
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