Tracking ultrafast chiral dynamics requires two key ingredients: a source of chiral light pulses, and a light-matter interaction scheme producing chiro-sensitive signals. These two elements have been developed in parallel during the project, resulting in a variety of schemes addressing complementary aspects of molecular chirality.
One of the pillars of the project is the development of a new circularly polarized attosecond light source in the extreme ultraviolet range, based on very high repetition rate lasers. We have purchased a new laser system and developed a new beamline to produce extremely bright extreme ultraviolet pulses, reaching record photon fluxes. We have compared different strategies to produce circularly polarized radiation. This source has been coupled to a new coincidence imaging electron-ion spectrometer, which has been built within the project, and is now used for chiral photoionization experiments.
We initially thought that tracking attosecond chiral dynamics could only be possible using attosecond extreme ultraviolet pulses. However we found several ways of measuring such dynamics with strong femtosecond laser pulses: the temporal resolution is in that case not given by the pulse duration but by the oscillation period of the electric field. We have demonstrated that significant chiral responses could be measured in this strong field regime. We have then used photoelectron interferometry to measure a tiny difference between the time it takes for an electron to leave a chiral molecule or its mirror image, when ionized by circularly polarized light (only 7 attoseconds). Next we have combined multiple electric fields to sculpt a light field whose rotation direction switches every few hundreds of attoseconds. While this field carries zero net chirality, we have demonstrated that the ionized electrons could be deeply affected by its instantaneous chirality, stressing the ultrashort character of the photoionization process. This scheme has enabled us to discover that quantum tunneling through a rotating potential barrier was sensitive to the chirality of the barrier. Last, we have used elliptically polarized strong laser fields to drive ionized electrons to re-collide with their parent ion and measured laser-induced chiral rescattering.
In parallel to the investigation of the attosecond chiral photoionization process, we have tracked the ultrafast relaxation of photoexcited chiral molecules by chiral femtochemistry. We have discovered that in chiral molecules, bound wavepackets produced by circularly polarized light show a very strong asymmetry, leading to a new type of chiral observable we called photoexcitation circular dichroism. We showed that this observable was an extremely sensitive probe of ultrafast electronic chiral dynamics.
Last, we have performed extensive studies of the resonant multiphoton ionization of chiral molecules, benefiting from the high-repetition rate of the laser. We have discovered a new way to measure enantiomeric excesses in chemical samples with unprecedented speed and accuracy using photoelectron elliptical dichroism. We have conducted fundamental investigations of this processes, and demonstrated its applicative potential.
