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Metal nanoparticles of about 4000 atoms are exposed to intense 130 fs optical single and double laser pulses (in the range 10^13-10^14 W/ cm^2). The detection system includes a newly developed momentum spectrometer which operates similar to a classical Thomson parabola spectrometer. However, the features of the new setup features are a practically underground free measurement which allows for a huge dynamic range, an improved energy resolution and a significantly enhanced transmission.
Charged resolved energy ion spectra from the laser-exposed Coulomb explosion of small silver clusters have been recorded. Under single laser pulse excitation conditions, multiply charged ions Ag q+ (up to q=14) with energies exceeding 14 keV have been detected. Optical delay studies show the impact of nanoplasmonic oscillations on the ionization dynamics which reflects in the ion charge states as well as the recoil energies. Under optimal pump-probe conditions, i.e. when the Mie-frequency of the expanding nanoplasma matches the laser-nanoparticle resonance, significantly higher charge states (up to q=19) and more energetic ions (up to 300 keV) are observed. The collective electron motion most pronounced at the plasmon resonance has an impact on the angular emission distribution of the ions. Especially the highly charged ions are predominantly emitted along the laser polarization axis.
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