Intense Extreme Ultraviolet Pulses for Attosecond Pump-Probe Experiments

Attosecond science enables the study of ultrafast dynamics on atomic scales, providing fundamental insights into light–matter interaction. This thesis work aims to advance the development and application of an attosecond light source capable of delivering extreme ultraviolet (XUV) pulses with exceptionally high intensity.High-order harmonic generation (HHG) is a nonlinear process where a strong laser—typically in the infrared (IR) spectral region—is focused into a gas target, producing attosecond pulses in the XUV spectral region. These pulses are commonly used in pump-probe experiments, where a pump pulse excites the system and a probe pulse interrogates the induced dynamics, allowing for time-resolved measurements of ultrafast processes.XUV–IR pump-probe schemes investigate electron dynamics via interactions that involve a single XUV and several infrared photons. However, infrared-driven processes can add complexity to the interpretation of the induced dynamics. In contrast, XUV–XUV pump-probe schemes provide a more direct approach, in which single-photon-induced dynamics are probed by a single second photon. Reaching the regime in which two XUV photons are absorbed requires high intensities, but the inherently low conversion efficiency of HHG poses a major challenge. To overcome this limitation, generation conditions, phase-matching conditions, and the wavefront characteristics of the driving field must be optimized.This thesis demonstrates advancements in generating intense attosecond XUV pulses by optimizing the HHG process. Additionally, it explores how generation conditions affect the harmonic focus position and waist, influencing the ability to refocus the XUV pulses to a high-intensity spot. Beyond source optimization, applications of intense attosecond pulses in XUV–XUV and XUV–IR pump-probe experiments are investigated, enabling studies of electron dynamics upon photoionization. These experiments provide new insights into photoionization and ultrafast charge migration, enhancing our understanding of attosecond dynamics.By refining attosecond pulse generation, this thesis contributes to the next generation of high-intensity ultrafast light sources, opening new possibilities for time-resolved studies in atomic and molecular physics.