16 Octobre – Thesis defense - Étienne Bloch

14 h Amphi D - Building A29 (Talence campus)

Étude des dynamiques chirales femtosecondes et attosecondes par imagerie de vecteur vitesse et spectroscopie de photoelectrons et photoions en coïncidence.

The absence of mirror symmetry in the structure of a molecule, or chirality, is of fundamental importance in a broad range of fields, from biology, chemistry, drug synthesis, and physics. It is investigated here at its natural timescale, from femtosecond ($10^{-15}$ s) to attosecond ($10^{-18}$ s), by the use of ultrashort laser pulses. When a chiral molecule is ionized by a circularly polarized laser field, strong chirosensitive asymmetries can appear in the photoelectron angular distribution, namely photoelectron circular dichroism.
We will see here how new generation high repetition rate laser beamline can be employed with a velocity map imaging spectrometer or a photoelectron-photoion coincidence spectrometer in order to access these asymmetries. The light-matter interaction will be investigated in two regimes. One the one hand, multiphoton ionization shows a high molecular sensitivity. Elliptically polarized fields will be used in particular to study the mechanisms of anisotropy of excitation. Fragmentation-dependent processes will be resolved with the coincidence detection, and femtosecond dynamics will be accessed by using time-resolved pump-probe schemes. On the other hand, strong field ionization provides a simplified semi-classical framework. It will be used to unravel the sub-optical cycle light-matter interaction at the origin of chiroptical processes by the use of tailored vectorial laser fields. This will enable us to understand how the individual photoelectron trajectories are imprinted with chirality, while enriching the strong-field toolbox with a highly sensitive observable.

Event localization