Correlated two-electron dynamics in strong-field double ionization

Abstract

Vector momenta of electrons and ions have been measured for strong-field (25 fs, 0.25 to 1.0 ${\mathrm{P}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}$) double ionization of Ar using a ``reaction microscope.'' Correlated two-electron momentum distributions along the field direction ${(P}_{1\ensuremath{\parallel}}{,P}_{2\ensuremath{\parallel}})$ are explored at different transverse momenta ${P}_{1\ensuremath{\perp}}$ of one of the electrons. Whereas a distinct ${(P}_{1\ensuremath{\parallel}}{,P}_{2\ensuremath{\parallel}})$ correlation, strongly varying with ${P}_{1\ensuremath{\perp}}$ is observed for nonsequential double ionization at small light intensity, only a weak, but still significant correlation is found at large intensity where sequential ionization dominates.