Ionization and Coulomb explosion of xenon clusters by intense, few-cycle laser pulses

Intense, ultrashort pulses of 800 nm laser light (12 fs, ~4 optical cycles) of peak intensity 5× 10<SUP>14</SUP> W cm<SUP>-2</SUP> have been used to irradiate gas-phase Xe<SUB>n</SUB> clusters (n=500-25 000) so as to induce multiple ionization and subsequent Coulomb explosion. Energy distributions of exploding ions are measured in the few-cycle domain that does not allow sufficient time for the cluster to undergo expansion due to Coulombic and hydrodynamic pressures. This results in overall dynamics that appear to be significantly different to those in the many-cycle regime. One manifestation is that the maximum ion energies are measured to be much lower than those obtained when longer pulses of the same intensity are used. Ion yields are cluster-size independent but polarization dependent in that they are significantly larger when the polarization is perpendicular to the detection axis than along it. This unexpected behavior is qualitatively rationalized in terms of a spatially anisotropic shielding effect induced by the electronic charge cloud within the cluster