Vector momentum distributions of Ne(n+) (n = 1,2,3) ions created by 30 fs, approximately 1 PW/cm(2) laser pulses at 795 nm have been measured using recoil-ion momentum spectroscopy. Distinct maxima along the light polarization axis are observed at 4.0 and 7.5 a.u. for Ne2+ and Ne3+ production, respectively. Hence, mechanisms based on an instantaneous release of two (or more) electrons can be ruled out as a dominant contribution to nonsequential strong-field multiple ionization. The positions of the maxima are in accord with kinematical constraints set by the classical "rescattering model."

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Intensity interferometry was applied to study electron correlations in doubly ionizing ion-atom collisions. In this method, the probability to find two electrons emitted in the same double ionization event with a certain momentum difference is compared to the corresponding probability for two uncorrelated electrons from two independent events. The ratio of both probabilities, the so-called correlation function, is found to sensitively reveal electron correlation effects, but it is rather insensitive to the collision dynamics.

The collision dynamics of He single ionization by 3.6 MeV/u Se 28ϩ impact was explored using the reaction microscope of the Gesellschaft für Schwerionenforschung, a high-resolution integrated multielectron recoil-ion momentum spectrometer. The complete three-particle final-state momentum distribution ͑nine Cartesian components p i ͒ was imaged with a resolution of ⌬p i ϷϮ0.1 a.u. by measuring the three momentum components of the emitted electron and the recoiling target ion in coincidence. The projectile energy loss has been determined on a level of ⌬E p /E p Ϸ10 Ϫ7 and projectile scattering angles as small as ⌬Ϸ10 Ϫ7 rad became accessible. The experimental data which are compared with results of classical trajectory Monte Carlo calculations reveal an unprecedented insight into the details of the electron emission and the collision dynamics for ionization of helium by fast heavy-ion impact.