LAUSR

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 interference between direct ionization channels and a resonant pathway, which passes through the ac-Stark-shifted state, and show how the underlying Rydberg state population depend on the field strength and pulse duration.