Atoms and clusters in strong laser fields
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Nijmegen : [S.n.]
Number of pages
Radboud Universiteit Nijmegen, 29 oktober 2008
Promotor : Vrakking, M.J.J.
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Molecular and Biophysics
SubjectMolecular and Biophysics
This thesis describes experimental and theoretical studies on the interaction of strong infrared laser fields with atoms and atomic clusters. Part I provides an overview of the main strong-field phenomena in atoms, molecules and clusters and describes the state-of-the-art in strong-field science. Part II is devoted to the phenomenon of above-threshold ionisation (ATI) in rare-gas atoms and describes the experimental results on ATI in Xenon and Argon in a wide range of laser wavelengths from 600 to 800 nm and from 1200 to 1600 nm. Photoelectron momentum spectra recorded with an imaging spectrometer are carefully reproduced in TDSE calculations. We have established the dominance of resonance-enhanced ionisation mechanism in the visible frequency range both in the multiphoton and in the tunnelling regimes. Additionally, we have observed two characteristic contributions in the electron momentum spectra, whose origin so far remained an open question. Preliminary analysis of these patterns has been performed and general trends on their evolution with the laser wavelength and intensity are described in detail. Part III presents the results of optimal-control experiments on the production of highly charged ions from large xenon clusters. The optimal pulse shape leading to the enhancement of the ionic charge states has been interpreted in terms of plasma resonance. In our numerical simulations of xenon clusters interacting with intense shaped laser pulses under control of a genetic algorithm we have identified the influence of several mechanisms in the optimal cluster explosion having their origin in molecular and plasma physics. Our results show how the physics of clusters evolves from dynamics of small molecules and provide insight into the onset of collective effects with increasing cluster sizes. Furthermore, we have demonstrated a possibility of performing an experiment on size-selected clusters, which will allow verification of the proposed mechanisms of the efficient laser-cluster energy coupling.
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