  We report on non-sequential double ionization of Ar by a laser pulse
consisting of two counter rotating circularly polarized fields (390 nm and 780
nm). The double ionization probability depends strongly on the relative
intensity of the two fields and shows a "knee"-like structure as function of
intensity. We conclude that double ionization is driven by a beam of nearly
monoenergetic recolliding electrons, which can be controlled in intensity and
energy by the field parameters. The electron momentum distributions show the
recolliding electron as well as a second electron which escapes from an
intermediate excited state of Ar$^+$.
