Measurement of energies of ions that result from disassembly of atomic and molecular clusters [${\text{Ar}}_n$, $n=2000–\mathrm{40\hspace{0.17em}000}$; ${\left({\mathrm{N}}_2\right)}_n$, $n=50–3000$] in strong optical fields provides evidence for “charge-flipping” acceleration that gives rise to ions with energies in excess of the Coulombic limit. Measurements of ion spectra as a function of cluster size, and as a function of laser polarization, demonstrate different facets of charge-flipping acceleration.

• Received 27 October 2003

DOI:https://doi.org/10.1103/PhysRevA.69.033202