Controlling Subcycle Optical Chirality in the Photoionization of Chiral Molecules

Abstract

Controlling the polarization state of electromagnetic radiation enables the investigation of fundamental symmetry properties of matter through chiroptical processes. Over the past decades, many strategies have been developed to reveal structural or dynamical information about chiral molecules with high sensitivity, from the microwave to the extreme ultraviolet range. Most schemes employ circularly or elliptically polarized radiation, and more sophisticated configurations involve, for instance, light pulses with time-varying polarization states. All these schemes share a common propertythe polarization state of light is always considered as constant over one optical cycle. In this study, we zoom into the optical cycle in order to resolve and control a subcyle attosecond chiroptical process. We engineer an electric field whose instantaneous chirality can be controlled within the optical cycle, by combining two phase-locked orthogonally polarized fundamental and second harmonic fields. While the composite field has zero net ellipticity, it shows an instantaneous optical chirality which can be controlled via the two-color delay. We theoretically and experimentally investigate the photoionization of chiral molecules with this controlled chiral field. We find that electrons are preferentially ejected forward or backward relative to the laser propagation direction depending on the molecular handedness, similarly to the well-established photoelectron circular dichroism process. However, since the instantaneous chirality switches sign from one half cycle to the next, electrons ionized from two consecutive half cycles of the laser show opposite forward/backward asymmetries. This chiral signal, termed here as ESCARGOT (Enantiosensitive Sub-Cycle Antisymmetric Response Gated by electric-field rOTation), provides a unique insight into the influence of instantaneous chirality in the dynamical photoionization process. More generally, our results demonstrate the important role of sub-cycle polarization shaping of electric fields, as a new route to study and manipulate chiroptical processes.

Spiral-like holographic structures: Unwinding interference carpets of Coulomb-distorted orbits in strong-field ionization

“…Matter in intense laser fields (I = 10 13 W/cm 2 or higher) has led to the inception of attoscience. Attoseconds are some of the shortest timescales in nature, which allows real-time probing of electron dynamics and, potentially, target reconstruction [1][2][3][4][5][6][7][8][9]. In order to reconstruct targets, one must measure both amplitudes and phase differences.…”

Laser-induced persistent orientation of chiral molecules

“…The related studies of gas phase chiral molecules focus on the measurements of enantiomeric excess, handedness of a given compound, and on devising techniques for manipulating mixtures containing both enantiomers [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In addition, over the years more ambitious directions were considered theoretically -laser assisted asymmetric synthesis, enantiomeric interconversion and purification (e.g.…”

Multichromatic Polarization-Controlled Pulse Sequences for Coherent Control of Multiphoton Ionization

“…For example, PLP bichromatic fields were applied to control plasmonenhanced photoemission from silver clusters [178] and strongfield photoemission from gold nanotips [79]. OLP bichromatic fields with commensurable frequencies, characterized by Lissajous-type polarization profiles which exhibit a timevarying optical chirality, have been used to investigate subcycle variations in the PECD of chiral molecules [179,180]. Commensurable CRCP bichromatic fields exhibit unique propeller shapes with distinct rotational symmetry.…”