Colloquium di Dottorato: Caterina Vozzi
High-order harmonics are generated from the interaction of intense femtosecond laser pulses with noble gases. Recently, high-order Harmonic Generation (HHG) led to the realization of table-top sources of coherent XUV and Soft-X Ray radiation. With these sources, ultrafast spectroscopy can be performed with extreme temporal resolutions, down to the attosecond regime (1 as = 10-18 s), and with the site and chemical selectivity. These features grant access to purely electronic dynamics in molecules and solids and fundamental processes of light-matter interaction. Furthermore, HHG has been successfully used as a spectroscopic tool in the gas phase and condensed matter, allowing the study of electron dynamics in a cation following sudden ionization, all-optical band structure reconstruction, and berry phase retrieval. These findings demonstrate the flexibility and potentiality of this technique.
In this colloquium, I will introduce the principle of high-order harmonic generation as a source of XUV radiation and its application for ultrafast XUV spectroscopy and high-order harmonic spectroscopy. I will also report on the most recent developments in ultrafast XUV spectroscopy based on HHG in the Udyni labs  at CNR-IFN.
I will describe our recent developments in efficient XUV generation in microfluidic devices fabricated by femtosecond laser irradiation followed by chemical etching . With this approach, we were able to control the harmonic generation process in the gas on the micro-meter scale with high flexibility, enabling a high photon flux and phase matching on broadband harmonics up to 200 eV. This source is part of a new beamline for transient absorption/reflectivity measurements in molecules and solids. I will also describe the beamline developed for HHG spectroscopy in solids available at CNR-IFN and report on preliminary results in dielectrics and semiconductors.
 A. G. Ciriolo et al., J. Phys. Photonics 2, 024005 (2020); https://doi.org/10.1088/2515-7647/ab7d81
 A. G. Ciriolo et al., APL Photonics 7, 110801 (2022); https://doi.org/10.1063/5.0118199