Evidence of ac-Stark-shifted resonances in intense two-color circularly polarized laser fields

We report on the appearance of a structure at low energies in the photoelectron momentum distribution of the hydrogen atom exposed to two-color counterrotating bicircular laser fields. These structures, which arise due to ac-Stark-shifted resonances, break the threefold symmetry, typical for the \ensuremath{\omega}\ensuremath{-}2\ensuremath{\omega}bicircular fields. We discuss the physical origin of this structure in terms of partial-wave...