During the first phase we developed a new two-foci beamline for transient absorption/reflection spectroscopy that was published in Rev. Sci. Instrum. (Lucarelli et al., 91, 053002 (2020)). This beamline, later upgraded for polarization-invariant operation (manuscript under preparation), allowed unprecedented delay calibration which was used to achieved attosecond spectroscopy experiments in bulk materials, probing ultrafast electron dynamics and laying the foundation for future studies. At first we resolved sub-femtosecond core-exciton dynamics in MgF2, discovering their dual atomic–solid nature which unfold on different, ultrafast, time scales never investigated before (Nat. Commun. 12, 1–7 (2021)).
Further experiments on insulators like diamond and LiF revealed new phenomena. In diamond, absolute timing allowed us to investigate coherent electron dynamics and show that vertical transitions of virtual charges play a key role, revising the picture of strong-field intra-band motion (Nat. Photonics 19, 999–1005 (2025)). The results suggest interpretation with Floquet theory, which has been tested against short pulses in a different experiment (Nat. Commun. 13, 7013 (2022)).
In LiF, a previously unseen excitonic resonance was detected. This transition, hidden in standard measurement, becomes detectable only under strong-field excitation, showing that light pulses can induce new functionalities on ultrafast time scales (manuscript in preparation).
The project then shifted to semiconductors. At ELETTRA, we characterized static properties of several materials, including MoS2, where contrary to expectations, no core-exciton transitions were found. Collaboration with theory attributed this to electron correlation and screening, resolving a currently debated matter (manuscript in preparation).
After synchrotron characterization, we performed attosecond spectroscopy on Ge under various conditions. The extreme time resolution allowed us to disentangle competing charge-injection mechanisms in intrinsic crystal, unravelling the process of ultrafast charge injection (Nat. Photonics 17, 1059–1065 (2023), Inzani et al., Nuovo Cim. C 46, 110 (2023), Di Palo et al., Stru. Dyn. 11, 044303 (2024)). The results obtained with doped samples, instead, proved the possibility to tune the timing of optical response and control real–virtual charge interplay (manuscript in preparation).
Parallel theoretical work advanced attosecond methodology, including two-color mapping (J. Phys. B 54, 154003 (2021); Phys. Rev. A 108, 013117 (2023)), volume-average effects (J. Phys. Photonics 4, 034006 (2022)), and iterative reconstruction (Opt. Express 29, 9711–9722 (2021), Opt. Express 30, 12248–12267 (2022), APL Photonics 8, 076101 (2023); J. Phys. Photonics 6, 025007 (2024)).
Finally, three reviews, summarizing the field, have been published (Borrego-Varillas et al., Rep. Prog. Phys. 85, 066401 (2022), Di Palo et al., APL Photonics 9, 020901 (2024); Inzani & Lucchini, J. Phys. Photonics 7, 022001 (2025)).
