29 research outputs found
Tracing Electron-Ion Recombination in Nanoplasmas Produced by Extreme- Ultraviolet Irradiation of Rare-Gas Clusters
We investigate electron-ion recombination in nanoplasmas produced by the
ionization of rare-gas clusters with intense femtosecond extreme-ultraviolet
(XUV) pulses. The relaxation dynamics following XUV irradiation is studied
using time-delayed 790-nm pulses, revealing the generation of a large number
of excited atoms resulting from electron-ion recombination. In medium-sized
Ar-Xe clusters, these atoms are preferentially created in the Xe core within
10 ps after the cluster ionization. The ionization of excited atoms serves as
a sensitive probe for monitoring the cluster expansion dynamics up to the ns
time scale
Rare-Gas Clusters in Intense Extreme-Ultraviolet Pulses from a High-Order Harmonic Source
We report evidence for two previously unidentified effects in the ionization
of rare-gas clusters by intense extreme-ultraviolet pulses. First, electron
spectra indicate multistep photoemission with increasing isotropy for larger
clusters due to electron-atom collisions. Second, very slow (meV) electrons
are interpreted as the first experimental evidence for Rydberg-like atomic
state formation in the nanoplasma expansion. Only small fractions of Xe2+ ions
were found, in sharp contrast to previous results recorded under comparable
conditions [Murphy et al., Phys. Rev. Lett. 101, 203401 (2008)]
Laser-Cluster-Interaction in a Nanoplasma-Model with Inclusion of Lowered Ionization Energies
The interaction of intense laser fields with silver and argon clusters is
investigated theoretically using a modified nanoplasma model. Single pulse and
double pulse excitations are considered. The influence of the dense cluster
environment on the inner ionization processes is studied including the lowering
of the ionization energies. There are considerable changes in the dynamics of
the laser-cluster interaction. Especially, for silver clusters, the lowering of
the ionization energies leads to increased yields of highly charged ions.Comment: 10 pages, 11 figure
Evolution of dopant-induced helium nanoplasmas
Two-component nanoplasmas generated by strong-field ionization of doped
helium nanodroplets are studied in a pump-probe experiment using few-cycle
laser pulses in combination with molecular dynamics simulations. High yields of
helium ions and a pronounced, droplet size-dependent resonance structure in the
pump-probe transients reveal the evolution of the dopant-induced helium
nanoplasma. The pump-probe dynamics is interpreted in terms of strong inner
ionization by the pump pulse and resonant heating by the probe pulse which
controls the final charge states detected via the frustration of electron-ion
recombination
Dynamics of free and embedded lead clusters in intense laser fields
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
Strong field dual-pulse excitation of Ag
The ionization of silver clusters exposed to pairs of
intense femtosecond laser pulses strongly depends on the optical delay.
Enhanced production of a certain atomic charge state z is obtained by a
z-dependent delay. This may open a possible
route to control the excitation process and populate specific
charge states. The optimum pulse separation which maximizes the generation
of highly ionized species varies by more than one order of magnitude when
the mean size of the clusters increases from to . Semiclassical Vlasov
simulations applied to a model system reveal the importance of the initial ionic
motion in the ionization process