title: Bicircular High-Harmonic Spectroscopy Reveals Dynamical Symmetries of Atoms and Molecules.
abstract: We introduce bicircular high-harmonic spectroscopy as a new method to probe dynamical symmetries of atoms and molecules and their evolution in time. Our approach is based on combining a circularly polarized femtosecond fundamental field of frequency ω with its counterrotating second harmonic 2ω. We demonstrate the ability of bicircular high-harmonic spectroscopy to characterize the orbital angular momentum symmetry of atomic orbitals. We further show that breaking the threefold rotational symmetry of the generating medium-at the level of either the ensemble or that of a single molecule-results in the emission of the otherwise parity-forbidden frequencies 3qω  (q∈N), which provide a background-free probe of dynamical molecular symmetries.
authors.affiliation: Laboratorium für Physikalische Chemie, ETH Zürich, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland.
authors.forename: Denitsa
authors.initials: D
authors.lastname: Baykusheva
authors.affiliation: Laboratorium für Physikalische Chemie, ETH Zürich, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland.
authors.forename: Md Sabbir
authors.initials: MS
authors.lastname: Ahsan
authors.affiliation: Laboratorium für Physikalische Chemie, ETH Zürich, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland.
authors.forename: Nan
authors.initials: N
authors.lastname: Lin
authors.affiliation: Laboratorium für Physikalische Chemie, ETH Zürich, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland.
authors.forename: Hans Jakob
authors.initials: HJ
authors.lastname: Wörner