Momentum Imaging of Electron Wave Packet Interference

The recent experiment by Gopal, {{\emph{et al.}}}[\emph{Phys. Rev. Lett.} \textbf{103}, 053001 (2009) ] detects intriguing interference patterns in the single ionization of helium by few-cycle, phase-stabilized IR laser pulses, which Gopal, {\emph{et al.}} interpret in terms of the coherent emission of distinct photoelectron wave packets within one IR cycle. By numerically solving the time-dependent Schr\"{o}dinger equation for the photoionization of helium within a single active electron model, we find interference fringes in the photoelectron momentum distribution that cannot be explained as above-threshold ionization peaks. We are in the process of analyzing these oscillations in the momentum-differential electron yield in terms of interfering photoelectron wave packets.