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1.
T. Döppner S. Teuber M. Schumacher J. Tiggesbäumker K.H. Meiwes-Broer 《Applied physics. B, Lasers and optics》2000,71(3):357-360
Clusters of heavy metal atoms in strong femtosecond laser-light fields undergo multi-ionization with the loss of hundreds
of electrons. The cross section largely exceeds that of corresponding isolated atoms, which leads in the case of PbN to a complete ionization of the 4f shell with a light intensity of 1.2×1015 W/cm2. Experimental investigations on Pb and Pt clusters with variable pulse widths and, for the first time, with the pump&probe
technique give insight into the dynamics of the coupling of electromagnetic radiation into the clusters. Both approaches support
the picture according to which, after an initial charging, the clusters expand due to Coulomb forces. This expansion is accompanied
by a reduction of the electron density and at the same time by an increase of the optical sensitivity. Once the plasmon energy
of the diluted nanoplasma approaches the photon energy, the charging efficiency increases significantly. The experimental
observations are confirmed by random-phase approximation (RPA) calculations of the optical response, including molecular-dynamics
simulations of the expanding systems.
Received: 11 November 1999 / Published online: 13 July 2000 相似文献
2.
The time-dependent response of simple metal clusters to femtosecond laser pulses is investigated using the semiclassical theory based on the Vlasov equation. Starting from a Thomas-Fermi ground state the dynamics are calculated by use of the pseudoparticle method. Systems studied here are sodium clusters containing up to 147 atoms. Both, the energy transfer to the cluster, which is largely affected by the plasmon enhanced absorption, and the following release of energy to the ions are examined in detail. During the laser excitation the feedback of the absorption to the development of the plasmon energy is controlled by competing mechanisms: ionization and cluster expansion. Characteristics of the Coulomb explosion are studied as function of photon energy and cluster size, particularly with regard to the dynamical influence of collective excitations of the electrons. We also predict features in the angular distribution of the ions that could be measured to test the calculated dynamics.Received: 9 December 2003, Published online: 16 March 2004PACS:
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.) - 36.40.Vz Optical properties of clusters - 36.40.Gk Plasma and collective effects in clusters 相似文献
3.
A simple model is developed that quantitatively describes intense interactions of a vacuum ultraviolet (VUV) laser pulse with a xenon cluster. We find good agreement with a recent experiment [Nature (London) 420, 482 (2002)]]. In particular, the large number of VUV photons absorbed per atom, at intensities significantly below 10(16) W/cm(2), is now understood. 相似文献
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高频强激光场中高价负离子(比如H-,H2-,He-,He2-等等)的稳定存在虽然在理论上早已得到得到证明,但在实验上至今没有被直接验证。为了探索可行的实验验证方案,通过以高频强场中的负一价氢离子H-为例,采用相空间平均法,详细研究了其在外加激光场中的电离率及光电子角分布情况。研究发现 的电离率比氢原子高,并且不存在氢原子在较强激光场中的电离抑制现象。另外随着激光场强度的增大和激光频率的减小,电子角分布与H-在高频场直接卸载后电子角分布的差别也增大。这些结果为将来在实验上验证高频强场中高价负离子的存在性提供了很好的理论依据。 相似文献
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Clusters of 2x10(3) to 4x10(4) Ar atoms are Coulomb exploded in intense (up to 8x10(15) W cm(-2)) laser fields. The dependence of multiply charged argon ion energies on the polarization state of light is probed. A directional asymmetry in the ion-explosion energies is observed for the highest charge states. The ion-energy distribution consists of a low-energy isotropic component, and a high-energy anisotropic one. The results are discussed in terms of an asymmetric Coulomb-explosion scenario. 相似文献
8.
T. Döppner S. Teuber Th. Diederich Th. Fennel P. Radcliffe J. Tiggesbäumker K. H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):157-160
Lead clusters are exposed to strong femtosecond light
pulses. The dependence of the recoil energy on the charge state
of the atomic ion is now investigated using a new detection
setup, i.e., a Thomson
analyser. First results show that in contrast to laser-induced
overdense plasmas at surfaces the recoil energy distribution
appears much narrower. Comparing free lead clusters with lead
clusters embedded in large helium droplets, the charging
dynamics show distinct differences on the femtosecond time
scale. In the embedded case the maximum ionization enhancement
is reached earlier. 相似文献
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T. Döppner J. P. Müller A. Przystawik J. Tiggesbäumker K.-H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):261-266
Silver clusters embedded in helium nanodroplets are
exposed to intense femtosecond laser pulses (1013 - 1016 W/cm2).
The signal of highly charged (q≤11) atomic fragments is maximized by
delayed plasmon enhanced ionization using stretched laser pulses. Further
details with respect to the dynamics of the charging process can be obtained,
when the intensity distribution within the laser focus is taken into
account. For the first time, the z-scan method is applied to clusters
which offers a route to investigate the explicit dependence of the ion signals
with respect to the laser intensity. By taking advantage of the volumetric
weighting effect ionization thresholds are determined, yielding values well
below 1014 W/cm2 for Agq+ ions with q≤11. 相似文献
11.
C. Peltz T. Fennel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,63(2):281-288
We theoretically investigate the impact of multiple plasmon resonances on the charging of
Xe clusters embedded in He nanodroplets under intense pump-probe laser excitation
(τ = 25 fs,
I
0 = 2.5 × 1014 W/cm2,
λ = 800 nm). Our molecular dynamics simulations on
Xe309He10 000 and comparison to results for free Xe309
give clear evidence for selective resonance heating in the He shell and the Xe cluster,
but no corresponding double hump feature in the final Xe charge spectra is found. Though
the presence of the He shell substantially increases the maximum charge states, the
pump-probe dynamics of the Xe spectra from the embedded system is similar to that of the
free species. In strong contrast to that, the predicted electron spectra do show
well-separated and pronounced features from highly efficient plasmon assisted electron
acceleration for both resonances in the embedded clusters. A detailed analysis of the
underlying ionization and recombination dynamics is presented and explains the apparent
disaccord between the resonance features in the ion and electron spectra. 相似文献
12.
A. Heidenreich I. Last J. Jortner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):195-202
We present a theoretical and computational study of the properties and the
response of the nanoplasma and of outer ionization in Xen clusters (n =
55–2171, initial cluster radius R0 = 8.7–31.0 ?) driven by
ultraintense near-infrared laser fields (peak intensity IM = 1015–1020 Wcm-2, temporal pulse length τ= 10–100 fs, and frequency ν= 0.35 fs-1). The positively charged high-energy nanoplasma produced by inner ionization nearly follows the oscillations of
the fs laser pulse and can either be persistent (at lower intensities of IM = 1015–1016 Wcm-2 and/or for larger cluster sizes, where the electron energy distribution is nearly thermal) or transient (at higher intensities
of IM = 1018–1020 Wcm-2 and/or for smaller cluster sizes). The nanoplasma is depleted by outer ionization that was semiquantitatively described by
the cluster barrier suppression electrostatic model, which accounts for the cluster size, laser intensity and pulse length
dependence of the outer ionization yield. The electrostatic model was further utilized for estimates of the laser intensity
and pulse
width dependence of the border radius R0
(I) for the attainment of complete outer ionization at
,
while at R0 > R0
(I) a persistent nanoplasma prevails. R0
(I)
establishes an interrelationship between electron dynamics and nuclear Coulomb explosion dynamics in ultraintense
laser-cluster interactions. 相似文献
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The interaction between intense femtosecond laser pulses
and hydrogen atomic clusters is studied by a simplified Coulomb
explosion model. The dependences of average proton kinetic energy on
cluster size, pulse duration, laser intensity and wavelength are
studied respectively. The calculated results indicate that the
irradiation of a femtosecond laser of longer wavelength on hydrogen
atomic clusters may be a simple, economical way to produce highly
kinetic hydrogen ions. The phenomenon suggests that the irradiation
of femtosecond laser of longer wavelength on deuterium atomic
clusters may be easier than that of shorter wavelength to drive
nuclear fusion reactions. The product of the laser intensity and the
squared laser wavelength needed to make proton energy saturated as a
function of the squared cluster radius is also investigated. The
proton energy distribution calculated is also shown and compared
with the experimental data. Our results are in agreement with the
experimental results fairly well. 相似文献
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A second plateau in the harmonic spectra of laser-driven two-electron atoms is observed both in the numerical solution of a low-dimensional model helium atom and using an extended strong field approximation. It is shown that the harmonics well beyond the usual cutoff are due to the simultaneous recombination of the two electrons, which were emitted during different, previous half-cycles. The new cutoff is explained in terms of classical trajectories. Classical predictions and the time-frequency analysis of the ab initio quantum results are in excellent agreement. The mechanism corresponds to the inverse single photon double ionization process in the presence of a (low frequency) laser field. 相似文献
19.
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. 相似文献
20.
The ionization of negative ions by ultrashort electromagnetic pulses, the multiphoton ionization of atoms beyond the perturbation
theory taking into account the Coulomb interaction, and the relativistic theory of tunneling in application to the ionization
problems have been analyzed. The main results have been obtained using the imaginary time method. 相似文献