XUV pump-XUV probe transient absorption spectroscopy at FELs

• Published in: Faraday discussions 2021-05, Vol.228, p.519-536
• Main Authors: Ding, Thomas, Rebholz, Marc, Aufleger, Lennart, Hartmann, Maximilian, Stooß, Veit, Magunia, Alexander, Birk, Paul, Borisova, Gergana Dimitrova, da Costa Castanheira, Carina, Rupprecht, Patrick, Mi, Yonghao, Gaumnitz, Thomas, Loh, Zhi-Heng, Roling, Sebastian, Butz, Marco, Zacharias, Helmut, Düsterer, Stefan, Treusch, Rolf, Ott, Christian, Pfeifer, Thomas
• Format: Article
• Language: English
• Subjects: Absorption spectra; Absorption spectroscopy; Coupling (molecular); Energy levels; Free electron lasers; Interferometry; Luminous intensity; Neon; Resolution; Spectrum analysis; Time lag; X ray spectra
• ISSN: 1359-6640; 1364-5498
• DOI: 10.1039/d0fd00107d

The emergence of ultra-intense extreme-ultraviolet (XUV) and X-ray free-electron lasers (FELs) has opened the door for the experimental realization of non-linear XUV and X-ray spectroscopy techniques. Here we demonstrate an experimental setup for an all-XUV transient absorption spectroscopy method for gas-phase targets at the FEL. The setup combines a high spectral resolving power of E /Δ E 1500 with sub-femtosecond interferometric resolution, and covers a broad XUV photon-energy range between approximately 20 and 110 eV. We demonstrate the feasibility of this setup firstly on a neon target. Here, we intensity- and time-resolve key aspects of non-linear XUV-FEL light-matter interactions, namely the non-resonant ionization dynamics and resonant coupling dynamics of bound states, including XUV-induced Stark shifts of energy levels. Secondly, we show that this setup is capable of tracking the XUV-initiated dissociation dynamics of small molecular targets (oxygen and diiodomethane) with site-specific resolution, by measuring the XUV transient absorption spectrum. In general, benefitting from a single-shot detection capability, we show that the setup and method provides single-shot phase-locked XUV pulse pairs. This lays the foundation to perform, in the future, experiments as a function of the XUV interferometric time delay and the relative phase, which enables advanced coherent non-linear spectroscopy schemes in the XUV and X-ray spectral range. A setup for an all-XUV transient absorption spectroscopy at free-electron lasers, was developed and employed to explore XUV-excited dynamics and XUV-driven nonlinear phenomena.