  At intensities below-the-recollision threshold, we show that
re-collision-induced excitation with one electron escaping fast after
re-collision and the other electron escaping with a time delay via a Coulomb
slingshot motion is one of the most important mechanisms of non-sequential
double ionization, for strongly-driven He at 400 nm. Slingshot-NSDI is a
general mechanism present for a wide range of low intensities and pulse
durations. Anti-correlated two-electron escape is its striking hallmark. This
mechanism offers an alternative explanation of anti-correlated two-electron
escape obtained in previous studies.
