Abstract
Energy distributions are measured for ions emitted upon Coulomb explosion of ${\mathrm{Ar}}_{n}$ clusters ($n=400\ensuremath{-}900$) upon irradiation by intense three-cycle pulses ($10$ fs) of $800$-nm laser light of peak intensity $5\ifmmode\times\else\texttimes\fi{}{10}^{14} \mathrm{W}\mathrm{ }{\mathrm{cm}}^{\ensuremath{-}2}$. With few-cycle pulses, there is insufficient time for the cluster to undergo expansion; this results in overall dynamics that are significantly different from those in the many-cycle regime. The peak ion energies are much lower than those obtained when $100$-fs pulses of the same intensity are used; they are almost independent of the size of the cluster (over the range $400\ensuremath{-}900$ atoms). Ion yields are measured to be larger in the direction that is perpendicular to the laser-polarization vector than along it. Model molecular dynamics calculations are used to qualitatively rationalize this unexpected anisotropy in terms of shielding by a spatially asymmetric electronic-charge cloud within the cluster.
Published Version
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