Dissertation / PhD Thesis

PUBDB-2026-00724

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Advances in High-Order Harmonic Sources and Applications to Free-Electron Laser Pulse Characterization

Azzolin, A. (Corresponding author)Extern*DESY* ; Calegari, F. (Thesis advisor)DESY* ; Drescher, M. (Thesis advisor)Extern*

2026

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Please use a persistent id in citations: urn:nbn:de:gbv:18-ediss-135077  doi:10.3204/PUBDB-2026-00724

Abstract: Attosecond and few-femtosecond light pulses provide the time resolution required to track and control the very first instants of electron dynamics in molecules and condensed matter. Since its first demonstration, High-order Harmonic Generation (HHG) sources have been at the core of experimental schemes aiming at unravelling ultrafast electron motion. This thesis reports advancements in high-order harmonic sources and their applications to both solid-state spectroscopy and Free-Electron Laser (FEL) pulse characterization. First, it demonstrates and rationalizes efficient soft X-ray HHG in the so-called overdriven regime enabled by a custom-designed differentially pumped glass chip. This development directly addresses some of the technical challenges of conventional high-photon-energy HHG sources, providing a more accessible approach. Second, this work presents results on solidstate High-order Harmonic Generation (sHHG) spectroscopy in crystalline, amorphous, and semi-periodic TiO2 samples. The experiment showcases the potential of HHG not only as a source, but also as a spectroscopic probe of the valence electrons governing materials functional properties. Finally, this thesis reports the experimental validation of Double-Blind Holography (DBH) of ultrashort FEL pulses. This is a fully optical platform for single-shot temporal haracterization, phase retrieval, and few-femtosecond resolution delay tagging that is based on the interference with an unknown external field, in this case a standard HHG source. Together, these developments extend the capabilities of high-order harmonic sources, opening new scenarios for investigating and controlling ultrafast electron dynamics in atoms, molecules and condensed matter, both with table-top schemes and at FELs.

Note: Dissertation, University of Hamburg, 2026

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Contributing Institute(s):

1. Attosecond Science and Technology (FS-ATTO)

Research Program(s):

1. 631 - Matter – Dynamics, Mechanisms and Control (POF4-631) (POF4-631)
2. 6G2 - FLASH (DESY) (POF4-6G2) (POF4-6G2)

Experiment(s):

1. Experiments at CFEL
2. FLASH2 Beamline FL26 (FLASH2)

Appears in the scientific report 2026

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