Vielteilchensimulation von Atomclustern in intensiven Laserfeldern

The interaction of atomic clusters with short, intense laser pulses has attracted both theoretical and experimental attention during the past decade. Experimental results indicate a more efficient transfer of laser energy into cluster matter as compared to gases and solids. These results include production of energetic electrons, XUV radiation and X-rays, highly charged energetic ions and neutrons from nuclear fusion Theoretical explanations of these findings are based on different approaches, many of which rely on the model of a cluster as a spherical plasma, which was developed by T. Ditmire et. al.. Accordingly several concepts familiar from plasma physics and strong field atomic physics are applied. Absorption by outer ionization, induced inverse bremsstrahlung, collisionless processes and linear and nonlinear dipole oscillations have been discussed. In this thesis the interaction of large atomic clusters consisting of more than 1000 atoms with laser pulses in the 10-100 fs regime and of intensities ranging from 10^15 W/cm^2 to 10^18 W/cm^2 is studied, with an emphasis on laser pulse absorption by outer ionization and the resulting electron and ion energy spectra. The cluster is described as an ideal collisionless plasma. The dynamics of the system is examined in the framework of a classical particle simulation. Pairwise particle interactions are calculated using a multipole approximation scheme developed in astrophysics which is known as a "tree code". Examination of free and laser driven collective electron oscillations shows that the Mie resonance can be excited due to ion expansion during the laser pulse. This resonance manifests itself by a jump in the relative phase between the laser field and the electron velocity. It is found that the cluster charge and the maximum kinetic energy of the ions are related linearly. Screening of the potential inside the expanding cloud of free electrons can be identified. Exact electrostatic equilibria of electrons residing inside the cluster are derived in the context of outer ionization. Based on these equilibria an analytic description of the outer ionization degree for immobile ions is found. This description is extended to the case of expanding ions. The laser amplitude required for complete outer ionization is greatly reduced in this case. Energy distributions of the electrons are classified according to the existence of a broad plateau for low laser intensity which does not occur for high laser intensity. The plateau reaches up to three times the quiver energy of an electron in the laser field. The case of high laser intensity is treated in the framework of a quasistatic model known from multiphoton ionization of atoms in strong laser fields.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2006

Author dc:creator

• Arndt, Ludwig Johannes

Contributors dc:contributor

• Kull, Hans-Jörg

• info:eu-repo/classification/ddc/530
• Physik
• Edelgascluster
• Laser
• Simulation
• cluster

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-120920%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:59106