Plasmon-Enhanced Multi-Ionization of Small Metal Clusters in Strong Femtosecond Laser Fields

Köller, L.; Schumacher, Mathias; Köhn, Jörg; Teuber, S.; Tiggesbäumker, J.; Meiwes‐Broer, Karl‐Heinz

doi:10.1103/physrevlett.82.3783

Cited by 149 publications

(146 citation statements)

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“…It is only for large rare gas clusters, with N ∼ 10 3 or more, that we expect a transition to a nanoplasma behavior, as it has been found in hydrodynamical simulations of such systems [4,12]. Where and how this transition happens will be the subject of further studies as well as the connection with enhanced energy absorption recently reported for small metal clusters [13].…”

supporting

confidence: 55%

Electron Release of Rare-Gas Atomic Clusters under an Intense Laser Pulse

Siedschlag

Rost

2002

Phys. Rev. Lett.

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Calculating the energy absorption of atomic clusters as a function of the laser pulse length T we find a maximum for a critical T * . We show that T * can be linked to an optimal cluster radius 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 * .After a basic understanding of the mechanisms governing atoms and molecules subjected to an intense laser pulse [1,2], analogous studies on clusters pioneered by Rhodes [3] and Ditmire [4] have appeared over the last years with a recent spectacular culmination in the demonstration of deuterium fusion in clusters [5]. Most of these studies do focus on the situation after the laser pulse, namely on the abundance and kinetic energy spectra of electrons and ions. Some discussion has been devoted to the question if the expansion of the cluster is driven by hydrodynamics or by a Coulomb explosion. Only very little attention has been paid to this type of dynamics in the time domain [6,7]. This is even more surprising since the time scales involved show that the expansion of the nuclei occurs on the same time scale as the pulse lengths which can be chosen, namely some 10 to 1000 fs, or roughly 10 −3 atomic units (which we will use hereafter). Apart from the nuclear motion and the pulse length T energy absorption from a laser pulse and subsequent ionization and fragmentation of the cluster involve two additional time scales, the optical cycle 2π/ω = 0.055a.u. for the typically used Titan-Sapphire laser of 800 nm wavelength, and the period of the bound electrons, which is of the order (hydrogen) of 1 a.u.. We will work with peak intensities between 10 14 − 10 16 W/cm 2 . In the following we will demonstrate that the seemingly complicated process of energy absorption and fragmentation in the laser pulse can be split into three different phases, an 'atomic ' phase I, a 'molecular' phase II, and a relaxation phase III. Phase I lasts for a time T 0 after the pulse has begun and is characterized by boiling off electrons through multiphoton or tunneling ionization, hence we have termed it 'atomic' phase. We define it to last until every second atom in the cluster has lost one electron, or equivalently until the probability of loosing an electron in an atom has reached p = 1/2. This probability is calculated from a Krainov tunneling rate [8] where, however, the instant electric field is formed by the laser and eventually already existing charged particles in the cluster.Up to T 0 we may assume that the atoms/ions have not moved yet. The second, molecular phase is characterized by Coulomb explosion of the cluster. During this phase, as we will show below, the cluster expands to a critical radius R * which o...

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supporting

confidence: 55%

Electron Release of Rare-Gas Atomic Clusters under an Intense Laser Pulse

Siedschlag

Rost

2002

Phys. Rev. Lett.

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“…Control of the absorption [17] and the emission characteristics by the pulse structure has been demonstrated with various schemes, e.g. stretched pulses [4,6,8,15], pumpprobe techniques [17,18,19,20], and multi-parameter pulse shaping [5,21]. Typically, resonant plasmon excitations lead to the emission of laser aligned energetic electrons [6,7,9] and highly charged atomic ions with high kinetic energy [8,20].…”

Section: Introductionmentioning

confidence: 99%

“…Under intense near-infrared laser pulses (λ ∼ 800 nm), the transition of gas-phase clusters into well-isolated finite nanoplasmas results in high energy absorption, rapid cluster explosion, and the emission of highly charged ions [3,4,5], fast electrons [6,7,8,9], and energetic photons from the vacuum ultraviolet up to the x-ray range [10,11,12,13,14]. Because of the opportunity to study the underlying ionization, heating, and decay mechanisms in a nearly background-free environment, intense laser-cluster interactions are of high interest also for various other fields ranging from plasma physics to applied laser-matter research.…”

Section: Introductionmentioning

confidence: 99%

Resonant charging of Xe clusters in helium nanodroplets under intense laser fields

Peltz

Fennel

2011

Eur. Phys. J. D

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Abstract. 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, I0 = 2.5 × 10 14 W/cm 2 , λ = 800 nm). Our molecular dynamics simulations on Xe309He10000 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.

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“…Hence, effects which depend on the internuclear distances can be resolved by varying the pulse length [11] and/or applying pump-probe techniques [12,13]. The resolution of an optimum time delay ∆t and the contrast of the signal in a pump-probe experiment increases if ∆t ≫ T , the length of each pulse.…”

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confidence: 99%

Surface-plasma resonance in small rare-gas clusters by mixing ir and vuv laser pulses

Siedschlag

Rost

2005

Phys. Rev. A

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The ionization dynamics of a Xenon cluster with 40 atoms is analyzed under a pump probe scenario of laser pulses where an infrared laser pulse of 50 fs length follows with a well defined time delay a VUV pulse of the same length and peak intensity. The mechanism of resonant energy absorption due to the coincidence of the IR laser frequency with the frequency of collective motion of quasi free electrons in the cluster is mapped out by varying the time delay between the pulses.In recent years, much work has been devoted to the ionization mechanisms of clusters in few-cycle, intense laser fields (i.e. pulse lengths of the order of 100 fs and intensities I = 10 13 . . . 10 16 W/cm 2 ): from the case of plasmon excitation when exposing metal clusters to relatively weak fields [1] over enhanced ionization akin of molecular ionization for small rare gas clusters in intense fields [3] to collective excitation of a plasma resonance in clusters of intermediate [4] to large sizes [5], ultimately leading to ionic charge states of 40+ and higher [6], thus potentially providing a new source for the generation of x-rays, energetic ions or electrons and, via nuclear fusion, even neutrons [7]. A new parameter regime for lasercluster interaction has been proven to become accesible with the first experiment using VUV-FEL light of 98nm wavelength for the ionization of rare gas clusters [8], soon followed by the first proposals for an explanation of the unexpectedly high charge states seen in this experiment [9,10].While XUV-cluster interaction is still the subject of an ongoing debate, there seems to be a more or less common understanding regarding the qualitative picture of IR laser-cluster interaction: during the rising part of the laser pulse, a few electrons are ionized [16] leaving the cluster with a net positive charge which leads to an expansion typically on the same time scale as the duration of the laser pulse. Hence, effects which depend on the internuclear distances can be resolved by varying the pulse length [11] and/or applying pump-probe techniques [12,13]. The resolution of an optimum time delay ∆t and the contrast of the signal in a pump-probe experiment increases if ∆t ≫ T , the length of each pulse. Since ∆t ≈ t c , the critical expansion time of the cluster at which maximum absorption of energy from the cluster pulse is possible, long times t c are desirable which implies large clusters consisting of heavy atoms (slower Coulomb explosion). Also, the large number of quasifree electrons temporarily trapped in the cluster, lead to a good contrast for the optimized versus non-optimized signal [13].The critical time t c originates from a critical radius R c = R(t c ) of the cluster, usually larger than the equilibrium radius R 0 , where energy absorption is most efficient. For larger clusters (resonant mechanism) this radius is determined by the surface plasma frequency approximately given bywhere N t is the number of atoms/ions in the cluster, Z t is their average charge, R t is the cluster radius and ω pl the bulk ...

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Plasmon-Enhanced Multi-Ionization of Small Metal Clusters in Strong Femtosecond Laser Fields

Cited by 149 publications

References 18 publications

Electron Release of Rare-Gas Atomic Clusters under an Intense Laser Pulse

Electron Release of Rare-Gas Atomic Clusters under an Intense Laser Pulse

Resonant charging of Xe clusters in helium nanodroplets under intense laser fields

Surface-plasma resonance in small rare-gas clusters by mixing ir and vuv laser pulses

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