Two-Pulse Field-Free Orientation Reveals Anisotropy of Molecular Shape Resonance

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 (omega) and two-color (omega + 2 omega) 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.