title: Two-pulse field-free orientation reveals anisotropy of molecular shape resonance.
abstract: We report the observation of macroscopic field-free orientation, i.e., more than 73% of CO molecules pointing in the same direction. This is achieved through an all-optical scheme operating at high particle densities (>10(17)  cm(-3)) that combines one-color (ω) and two-color (ω+2ω) nonresonant femtosecond laser pulses. We show that the achieved orientation solely relies on the hyperpolarizability interaction as opposed to an ionization-depletion mechanism, thus, opening a wide range of applications. The achieved strong orientation enables us to reveal the molecular-frame anisotropies of the photorecombination amplitudes and phases caused by a shape resonance. The resonance appears as a local maximum in the even-harmonic emission around 28 eV. In contrast, the odd-harmonic emission is suppressed in this spectral region through the combined effects of an asymmetric photorecombination phase and a subcycle Stark effect, generic for polar molecules, that we experimentally identify.
authors: Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland.
authors: P M
authors: PM
authors: Kraus
authors: Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland.
authors: D
authors: D
authors: Baykusheva
authors: Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland.
authors: H J
authors: HJ
authors: Wörner