Chirality in high-harmonic generation spectroscopy of molecules and solids

Chirality is the property of an object that cannot be superimposed with its mirror image by any translation or rotation. This property plays a crucial role in the biological activities of molecules and in the optical and magnetic properties of materials. This review will show recent advances in the study of ultrafast chiral processes occurring in molecular systems and materials investigated by high-order harmonic generation (HHG) spectroscopy, both from a theoretical and experimental point of view. HHG is a highly nonlinear optical process providing coherent XUV radiation with attosecond duration. The chemical physics community, in its broadest sense, has developed an interest in HHG spectroscopy, given the increasing number of studies of complex molecules, including those of biological relevance, chemical reactions, and characterization of the structure of solids by means of an ultrafast probe. Indeed, HHG is a powerful tool to capture the photoinduced electron dynamics in their natural timescale, also enabling the investigation of transient chirality, which is so far mostly unexplored. The study of chirality on the ultrafast timescale represents an opportunity to bridge the gap between atomic physics, chemical physics, and materials science in their traditional definitions and gain insight into fundamental chiral processes at the electron level.