The possibility to manipulate the electrical properties of matter with very short optical pulses is a fascinating field of research. For example, the interaction with light pulses can be used to deeply affect the electro-optical properties of the target through the creation of excitons: electron-hole quasi-particles formed by Coulomb interaction . Acquiring a detailed understanding of their dynamic nature is essential to promote their exploitation in advanced technological areas. In particular, the ultrafast processes unfolding at the femto- and attosecond domain are of primary relevance in view of the desired extension towards the petahertz regime. In my talk I will introduce the attosecond transient reflection spectroscopy and show how it can be used to investigate these dynamics by presenting our experimental study of core-excitons in a prototype wide-gap insulator: MgF2 . In combination with theoretical simulations, our results show that the excitonic quasi-particle exhibits a dual nature. On the few-fs time scale the exciton can be described with an atomic model, while the dynamics which unfold on a faster, attosecond, time scale cannot be explained if its solid nature is neglected.
References  L.V. Butov, Superlattices Microstruct. 108, 2–26 (2017).  M. Lucchini, et al., Nat. Commun. 12, 1021 (2021)