Anisotropic “charge-flipping” acceleration of highly charged ions from clusters in strong optical fields

Abstract

The disassembly of molecular clusters (N 2 ) n (n=50-3000) in strong optical fields is investigated using two-dimensional time-of-flight spectrometry. Very highly charged ions are formed with a two-component energy distribution. A low-energy, isotropic component correlates with Coulomb explosion. A highenergy, anisotropic component, that results from a "charge flipping" acceleration mechanism, gives rise to ions with energies in excess of the Coulombic limit.

Physical parameter dependence of the X-ray generation in intense laser–cluster interaction

“…As an example, new theoretical implementation has been recently proposed by Megi et al [9] showing the importance of electrons -surface collisions in the heating process and so far neglected. On another side, recent experimental results [10,11,12] on ion and/or electron angular distributions show, besides a disagreement with previous measurements [1], an anisotropy of the emission, which is not account for within the nanoplasma model [5]. All of these studies related to ion or electron emission are connected to both the dynamics of the induced plasma and the cluster explosion.…”

Anomalous Anisotropy in the Explosion of Rare-Gas Clusters Irradiated with Intense Few-Cycle Laser Pulses

“…This fact indicates a competition between physical processes driving cluster expansions on different time-scales. For longer pulse durations in the adiabatic regime, the anisotropy with degree of E 90 • /E 0 • < 1 can be explained by mechanisms such as surface polarisation acceleration [7] and the "charge-flipping" process [5,16]. However, these mechanisms are not expected to be significant in the non-adiabatic regime for the following reasons.…”

“…Fast highly-charged ions [3][4][5][6], electrons with energies in the keV range [7,8] and energetic x-rays [9][10][11] have been observed after explosions of clusters subject to strong laser fields. Most of these earlier experiments were performed with pulses of durations τ of 100s of fs, which is comparable to a typical cluster expansion time t E [2,11].…”

“…In the hydrodynamic expansion of large Xe clusters [7,14] a surface polarisation pressure with cos 2 θ angular dependence is believed to be responsible for the anisotropic cluster expansion (θ is the angle between the laser polarisation axis and the ion emission direction). In the case of Ar and N 2 clusters exploding predominantly by Coulomb forces [4,5] the asymmetry of highly energetic ions has been interpreted using a "charge-flipping" mechanism resulting from a time-dependent ion charge state [5,16], and the presence of higher charge states at θ = 0…”

Source X par agrégats : contrôle et optimisation des paramètres gouvernant l'interaction laser de puissance–agrégats de gaz rare

“…Différents modèles ontété développés [7,8,9] pour expliquer les mécanismes d'absorption de l'énergie laser, la dissipation de cetté energie au sein de l'agrégat ainsi que le mode d'expansion de l'agrégat. Très récemment, de nouvelles expériences principalement dédiéesà l'étude de l'émission des ions et/ou desélectrons [10,11] remettent en cause certains points des modèles comme, par exemple, l'observation très controversée [10] d'un pic d'électrons chauds prédit par le modèle nanoplasma standard unidimensionnel [7].…”