Phd in PHYSICS

Thesis title: Exploring excited-state energy landscapes via Impulsive Raman spectroscopy

Ultrafast spectroscopy has revolutionized our ability to study physical and chemical transformations that occur on the atomic scale, capturing transient dynamics down to the femtosecond realm. These techniques employ sequences of ultrashort pulses for studying photo-induced dynamical processes in molecules and solid-state samples, in a time-resolved fashion. In this thesis, we report the development from scratch and the application of an optical setup optimized for Impulsive Stimulated Raman scattering (ISRS). We introduce the theory behind a perturbative description of nonlinear spectroscopies, and we leverage on the insights provided by this modelling to demonstrate -also from an experimental point of view- how to disclose the full ISRS potential. In this respect, we show how an ad-hoc two-color ISRS scheme enables accessing the sign of excited-state displacements, one of the most elusive properties of excited molecular energy landscapes, which rules light-driven structural rearrangements. On the same direction, we prove that joint control over pulse chirps is a powerful control knob for achieving state and species selectivity in ISRS. Building on the theoretical tools presented above and dedicated experimental setups, we also address fundamental questions regarding the temperature dependence of spontaneous vs coherent Raman responses, as well as on the modification of stimulated Raman lineshapes upon high-power excitations. Finally, we present two applications of stimulated Raman in materials science, unveiling the electrochemical behavior of zinc in diluted deep eutectic solvents -for applications in zinc-ion batteries- and the physical mechanisms ruling the ultraslow stabilization of hyperaged glasses. All together, these results yield significant advances in the field of ultrafast vibrational spectroscopy, providing novel paradigms for resonant and non-resonant ISRS while answering questions pertaining both to fundamental and applied Physical Chemistry.