Photoexcitation circular dichroism in chiral molecules

• Published in: Nature physics Vol. 14; no. 5; pp. 484 - 489
• Main Authors: Beaulieu, S., Comby, A., Descamps, D., Fabre, B., Garcia, G. A., Géneaux, R., Harvey, A. G., Légaré, F., Mašín, Z., Nahon, L., Ordonez, A. F., Petit, S., Pons, B., Mairesse, Y., Smirnova, O., Blanchet, V.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2018; Nature Publishing Group
• Subjects: 119/118; 140/125; 639/766/36/1121; 639/766/36/1122; Atomic; Chemical Physics; Chiral dynamics; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Dichroism; Electric fields; Electrons; Light; Magnetic effects; Magnetic fields; Magnetic properties; Mathematical and Computational Physics; Metamaterials; Molecular; Molecular chains; Optical and Plasma Physics; Particle physics; Photoabsorption; Photoexcitation; Physics; Physics and Astronomy; Polarized light; Theoretical
• ISSN: 1745-2473; 1745-2481; 1476-4636
• DOI: 10.1038/s41567-017-0038-z

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. Photoexcitation circular dichroism generates an ultrafast response in chiral molecules, with a much higher sensitivity than standard circular dichroism.