We make use of an inhomogeneous electrostatic dipole field to impart a quantum-state-dependent deflection to a pulsed beam of OCS molecules, and show that those molecules residing in the absolute ground state, X1Σ+, ∣0000⟩, J=0, can be separated out by selecting the most deflected part of the molecular beam. Past the deflector, we irradiate the molecular beam by a linearly polarized pulsed nonresonant laser beam that impulsively aligns the OCS molecules. Their alignment, monitored via velocity-map imaging, is measured as a function of time, and the time dependence of the alignment is used to determine the quantum state composition of the beam. We find significant enhancements of the alignment (\costhetasqtd =0.84) and of state purity (>92%) for a state-selected, deflected beam compared with an undeflected beam.
@article{arxiv.1105.2413,
title = {Stark-selected beam of ground-state OCS molecules characterized by revivals of impulsive alignment},
author = {Jens H. Nielsen and Paw Simesen and Christer Z. Bisgaard and Henrik Stapelfeldt and Frank Filsinger and Bretislav Friedrich and Gerard Meijer and Jochen Küpper},
journal= {arXiv preprint arXiv:1105.2413},
year = {2017}
}