Chiral effects appear in a wide variety of natural phenomena and are of fundamental importance in science, from particle physics to metamaterials. The standard technique of chiral discrimination—photoabsorption circular dichroism—relies on the magnetic properties of a chiral medium and yields an extremely weak chiral response. Here, we propose and demonstrate an orders of magnitude more sensitive type of circular dichroism in neutral molecules: photoexcitation circular dichroism. This technique does not rely on weak magnetic effects, but takes advantage of the coherent helical motion of bound electrons excited by ultrashort circularly polarized light. It results in an ultrafast chiral response and the efficient excitation of a macroscopic chiral density in an initially isotropic ensemble of randomly oriented chiral molecules. We probe this excitation using linearly polarized laser pulses, without the aid of further chiral interactions. Our time-resolved study of vibronic chiral dynamics opens a way to the efficient initiation, control and monitoring of chiral chemical change in neutral molecules at the level of electrons.
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We thank R. Bouillaud and L. Merzeau for technical assistance. We thank M. Ivanov, F. Morales, A. Stolow and T. Elsaesser for stimulating discussions. We acknowledge financial support from the Agence Nationale pour la Recherche (ANR-14-CE32-0014 MISFITS), the University of Bordeaux and the Conseil Regional de Nouvelle-Aquitaine (2.1.3-09010502 COLA2 project). Z.M. and O.S. gratefully acknowledge the support from Deutsche Forschungsgemeinschaft, project Sm 292-5/1, A.G.H. gratefully acknowledges the support from Deutsche Forschungsgemeinschaft, projects IV 152/7-1 and HA 8552/2-1. A.F.O. and O.S. gratefully acknowledge the MEDEA project, which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement no. 641789 (H2020-MSCA-ITN-2014-641789-MEDEA (Marie Skłodowska Curie Innovative Training Networks)). S.B. acknowledges the support of a NSERC Vanier Canada Graduate Scholarship. R.G. acknowledges financial support from the Agence Nationale pour la Recherche through the XSTASE project (ANR-14-CE32-0010). The authors gratefully acknowledge the support of their collaboration through European Cooperation in Science and Technology (COST), programme CM1204 XLIC. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme no. 682978 - EXCITERS.
The authors declare no competing financial interests.
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Beaulieu, S., Comby, A., Descamps, D. et al. Photoexcitation circular dichroism in chiral molecules. Nature Phys 14, 484–489 (2018). https://doi.org/10.1038/s41567-017-0038-z