Probing molecular chirality and chiral dynamics using High Harmonic generation

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The main objective of our project is to develop new methods sensitive to molecular chirality, both its structure and dynamics. Our goals include resolving and controlling multielectron chiral dynamics in molecules at its natural, sub-femtosecond time-scale. So far, this ultrafast time-scale in chiral response has remained hidden in experiments. The proposed method is based on high harmonic generation from a gas of randomly oriented molecules (chiral HHG, cHHG). Its key component is the application of tailored intense pulses to induce, enhance and manipulate the chiral response.Chirality is a basic property of living matter, crucial for its function. Left and right enantiomers of molecules have identical chemical and physical properties unless they interact with another chiral object, such as chiral light. Traditional methods of chiroptical discrimination in rotationally isotropic media are linear spectroscopic techniques, which measure the difference of the optical response of left and right enantiomers to chiral (e.g. circularly polarized) light. In these techniques, the chiroptical effects arise from the interplay between the light-induced electric- and magnetic-dipole transitions. The magnetic effects in light-matter interaction are generally very weak. This results in a weak chiroptical response, often four to six orders of magnitude smaller than e.g. light absorption. The weakness of the chiral response poses challenges for time-resolved measurements.Constant efforts towards the enhancement of the chiral response have led to a remarkable recent progress in very challenging gas-phase studies. One of the most sensitive techniques is photoelectron circular dichroism spectroscopy, PECD, which heralded the "dipole revolution" in chiro-optical discrimination: chiral discrimination without using chiral light. Several new methods followed this remarkable breakthrough, working purely in electric dipole approximation, including enantio-sensitive microwave detection, photoexcitation circular dichroism (PXCD) and photoexcitation induced photoelectron circular dichroism (PXECD) . The concepts of PXCD and PXECD were developed in phase I of this proposal and involve ultrafast excitation and probing of chiral electronic or vibrational dynamics. Our theory provides a unified and simple description of all dipole-approximation based techniques and clarifies the mechanisms enabling chiral discrimination without chiral pulses. With this knowledge we are ready for the key new step: We propose to bring the "dipole revolution" to chiral HHG. With the new cHHGd method we aim to achieve high values of chiral dichroism – the hallmark of all dipole-based techniques, while also being able to simultanelously image the underlying chiral dynamics with the time resolution that is two orders of magnitude better than the available state-of-the art techniques.