Book of Abstracts Book of Abstracts - Universität Konstanz

Signatures of the Giant Dipole Resonance in the Response of Metal
Clusters for Strong-Field Dual-Pulse Excitation
Thomas Fennel, Tilo Döppner, Josef Tiggesbäumker and Karl-Heinz Meiwes-Broer
Institut für Physik, Universität Rostock, Universitätsplatz 3, 18051 Rostock , Germany
B - 31
The response of metal clusters irradiated with a sequence of two femtosecond laser pulses is
strongly dependent on the optical delay between the pulses. Recent experiments have shown
that the adjustment of the delay provides a powerful way to control the coupling of strong laser
radiation to finite systems. Both the yield of highly charged ions [1] as well as the kinetic
energy of emitted electrons is strongly enhanced for a particular optimal delay. The dynamics of
the signals is much more pronounced compared to earlier measurements using stretched
pulses [2].
For the investigation of the time-dependent interaction of dual pulses with simple metal clusters
numerical simulations have been performed using Thomas-Fermi-Vlasov molecular dynamics
(TFV-MD) [3]. The semiclassical treatment allows a fully three-dimensional microscopic
simulation of the laser-cluster interaction and provides a reasonable description of delocalized
electrons in the cluster groundstate as well as the violent nonlinear response to a strong field
close to TDLDA.
Simulations on Na55 and Ag55 show that also in the strong field regime the most effective
absorption is caused by resonant excitation of multi-plasmon modes. The calculations are in
qualitative agreement with the measurements and clearly reproduce an optimal optical delay for
enhanced ionization of the cluster [1], see Fig. 1, as well as a strong energy enhancement in the
electron emission.
Figure 1. (a) Calculated average charge of emitted ions after dual-pulse excitation of Na55 as a function of
the optical delay. Both pulses have a width of 50fs at a wavelength of 800nm. (b) Measured normalized
dual-pulse signals of Ag 5+ from the explosion of silver clusters in helium droplets, resulting from the
excitation with 130 fs pulses. Taken from Ref. [1].
References
[1] Döppner, Fennel et al., Phys. Rev. Lett, in press
[2] Köller, Schumacher, Köhn et al., Phys. Rev. Lett. 82:3783, 1999
[3] Fennel, Bertsch and Meiwes-Broer et al., Eur. Phys. J. D 29:367, 2004
71