Multichannel contributions in the nonsequential double ionization of CO2

Abstract

The intermediate molecular states in the double ionization of molecules by laser-driven electron recollision are encoded into the angular-dependent signature of the process. We identify through this signature the specific ionic states participating in the double-ionization mechanism. Using CO${}_{2}$ as an example we employ a 1350-nm strong field at $2\ifmmode\times\else\texttimes\fi{}{10}^{14}$ W cm${}^{\ensuremath{-}2}$ to ensure that nonsequential double ionization (NSDI) is the exclusive mechanism in CO${}_{2}^{2+}$ formation. Under these conditions we obtain two main results. First, the shape of the recolliding electron wave packet is inferred from measurements of the ellipticity dependence of the signal, and second, the inelastic recollision cross section in the molecular frame is extracted from the variation of the signal as a function of the angle between strong-field probe polarization and molecular axis. These results provide an angularly resolved electron-ion collision measurement in CO${}_{2}$ and demonstrate contributions to NSDI from both ground and first excited ionic states.