Revealing the influence of molecular chirality on tunnel-ionization dynamics

Strong-field light-matter interaction enables probing atomic and molecular structures and dynamics with unprecedented resolutions. The primary event common to all strong-field spectroscopies is tunnel-ionization through the target potential barrier lowered by the laser field. The tunneling dynamics and the complex properties of the outgoing electron are difficult to isolate from its subsequent scattering onto the ionic potential. To reveal them, we have performed a joint experimental and theoretical study using a specific target: chiral molecules, whose photoionization by circularly polarized light produces forward-backward asymmetric electron distributions with respect to the light propagation direction. These asymmetric patterns provide a background-free signature of the chiral potential in the ionization process.

We first implemented the attoclock technique, in which the released electrons are angularly streaked by the rotating laser field. We found that a strong forward-backward asymmetry in the electron yield is imprinted by chiral potential during the tunnel-ionization process. The subsequent scattering of the freed electron onto the chiral potential leads to an asymmetric angular streaking of the electron distribution. To access the phase of the tunneling wavepackets, we used photoelectron interferometry. We employed an orthogonally polarized two-color laser field whose optical chirality was manipulated on a sub-laser-cycle timescale. This scheme reveals that the combined action of the chiral potential and rotating laser field not only imprints asymmetric ionization amplitudes during the tunneling process, but also induces a forward-backward asymmetric phase profile onto the outgoing electron wave packets. Chiral light-matter interaction thus induces subtle angular-dependent shaping of both the amplitude and the phase of tunneling wave packets.