More than two decades ago, a theoretical proposal was made to distinguish the two mirror images of a chiral molecule with high contrast using colliding electrons. The corresponding electron-beam diffraction experiment was never performed because it requires controlling the orientation of the molecules with respect to the electron beam, which is difficult in the gas phase. Here, we show that the development of attosecond spectroscopy techniques offers an unexpected solution to this issue through chiral laser-induced electron diffraction measurements.

The oscillating electric field of a strong laser pulse tears electrons off a molecule, accelerates them, and drives them back toward their parent ion within a few femtoseconds. The electrons are then diffracted by the molecular potential, precisely encoding its structure and dynamics. Using elliptically polarized laser pulses, we show that laser-induced electron diffraction is sensitive to the chirality of the target. The field selectively ionizes molecules of a given orientation and drives the electrons along different sets of trajectories, leading them to recollide from different directions. Depending on the handedness of the molecule, the electrons are preferentially diffracted forward or backward along the light propagation axis. This asymmetry, we find, can reach several percent.

The chiral sensitivity of laser-induced electron diffraction opens a new path to resolve ultrafast chiral dynamics, with an attosecond temporal resolution dictated by the duration of the recolliding electron wave packet.