Three Dimensional Orientation of Complex Molecules Excited by Two-Color Femtosecond Pulses

TL;DR

This paper investigates how two-color femtosecond laser pulses can induce three-dimensional orientation in asymmetric-top molecules, including chiral ones, with potential applications in enantiomer separation.

Contribution

It demonstrates classical and quantum enantioselective orientation of chiral molecules using two-color pulses, with analysis of interaction potentials and long-lasting orientation effects.

Findings

Classical and quantum results agree on short time scales.

Enantioselective orientation causes opposite directions for enantiomers.

Quantum beats observed in long-term enantioselective orientation.

Abstract

We study the excitation of asymmetric-top (including chiral) molecules by two-color femtosecond laser pulses. In the cases of non-chiral asymmetric-top molecules excited by an orthogonally polarized two-color pulse, we demonstrate, classically and quantum mechanically, three-dimensional orientation. For chiral molecules, we show that the orientation induced by a cross-polarized two-color pulse is enantioselective along the laser propagation direction, namely, the two enantiomers are oriented in opposite directions. On the short time scale, the classical and quantum simulations give results that are in excellent agreement, whereas on the longer time scale, the enantioselective orientation exhibits quantum beats. These observations are qualitatively explained by analyzing the interaction potential between the two-color pulse and molecular (hyper-)polarizability. The prospects for utilizing the long-lasting orientation for measuring and using the enantioselective orientation for separating the individual enantiomers are discussed.