  We report a joint experimental and theoretical study of a three-sideband
(3-SB) modification of the "reconstruction of attosecond beating by
interference of two-photon transitions" (RABBIT) setup. The 3-SB RABBIT scheme
makes it possible to investigate phases resulting from interference between
transitions of different orders in the continuum. Furthermore, the strength of
this method is its ability to focus on the atomic phases only, independent of a
chirp in the harmonics, by comparing the RABBIT phases extracted from specific
SB groups formed by two adjacent harmonics. We verify earlier predictions that
the phases and the corresponding time delays in the three SBs extracted from
angle-integrated measurements become similar with increasing photon electron
energy. A variation in the angle dependence of the RABBIT phases in the three
SBs results from the distinct Wigner and continuum-continuum coupling phases
associated with the individual angular momentum channels. A qualitative
explanation of this dependence is attempted by invoking a propensity rule.
Comparison between the experimental data and predictions from an R-matrix
(close-coupling) with time dependence calculation shows qualitative agreement
in the observed trends.
