  We measure the photoelectron energy spectra from strong-field ionization of
Kr in a two-color laser pulse consisting of a strong 400-nm field and a weak
800-nm field. The intensities of the main above-threshold ionization (ATI) and
sideband peaks in the photoelectron energy spectra oscillate roughly oppositely
with respect to the relative phase between the two-color components. We study
the photoelectron interferometry in strong-field ATI regime from the view of
interference of different electron trajectories in order to extend RABBITT type
analysis to the strong-field regime. Based on the strong-field approximation
model, we obtain analytical expressions for the oscillations of both ATI and
sideband peaks with the relative phase. A phase shift of \pi/4 with respect to
the field maximum of the two-color laser pulse is revealed for the interference
maximum in the main ATI peak without including the effect of the atomic
potential.
