ORCID Profile
0000-0001-8611-4735
Current Organisation
Università degli Studi di Milano
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Publisher: American Physical Society (APS)
Date: 30-12-2016
Publisher: Elsevier BV
Date: 07-2006
Publisher: MDPI AG
Date: 16-06-2017
DOI: 10.3390/APP7060621
Publisher: International Union of Crystallography (IUCr)
Date: 21-04-2015
DOI: 10.1107/S1600577515005743
Abstract: The Low Density Matter (LDM) beamline has been built as part of the FERMI free-electron laser (FEL) facility to serve the atomic, molecular and cluster physics community. After the commissioning phase, it received the first external users at the end of 2012. The design and characterization of the LDM photon transport system is described, detailing the optical components of the beamline.
Publisher: American Physical Society (APS)
Date: 17-12-2018
Publisher: American Physical Society (APS)
Date: 19-06-2019
Publisher: Springer Science and Business Media LLC
Date: 14-02-2020
DOI: 10.1038/S41467-020-14721-2
Abstract: The recent development of ultrafast extreme ultraviolet (XUV) coherent light sources bears great potential for a better understanding of the structure and dynamics of matter. Promising routes are advanced coherent control and nonlinear spectroscopy schemes in the XUV energy range, yielding unprecedented spatial and temporal resolution. However, their implementation has been h ered by the experimental challenge of generating XUV pulse sequences with precisely controlled timing and phase properties. In particular, direct control and manipulation of the phase of in idual pulses within an XUV pulse sequence opens exciting possibilities for coherent control and multidimensional spectroscopy, but has not been accomplished. Here, we overcome these constraints in a highly time-stabilized and phase-modulated XUV-pump, XUV-probe experiment, which directly probes the evolution and dephasing of an inner subshell electronic coherence. This approach, avoiding any XUV optics for direct pulse manipulation, opens up extensive applications of advanced nonlinear optics and spectroscopy at XUV wavelengths.
Publisher: IOP Publishing
Date: 07-09-2015
Publisher: IOP Publishing
Date: 07-09-2015
Publisher: Elsevier BV
Date: 08-2012
Publisher: IOP Publishing
Date: 18-08-2006
Publisher: American Physical Society (APS)
Date: 20-02-2014
Publisher: Springer Science and Business Media LLC
Date: 10-01-2014
DOI: 10.1038/SREP03621
Abstract: Free electron lasers (FELs) offer the unprecedented capability to study reaction dynamics and image the structure of complex systems. When multiple photons are absorbed in complex systems, a plasma-like state is formed where many atoms are ionized on a femtosecond timescale. If multiphoton absorption is resonantly-enhanced, the system becomes electronically-excited prior to plasma formation, with subsequent decay paths which have been scarcely investigated to date. Here, we show using helium nanodroplets as an ex le that these systems can decay by a new type of process, named collective autoionization. In addition, we show that this process is surprisingly efficient, leading to ion abundances much greater than that of direct single-photon ionization. This novel collective ionization process is expected to be important in many other complex systems, e.g. macromolecules and nanoparticles, exposed to high intensity radiation fields.
Publisher: IOP Publishing
Date: 08-2020
Abstract: The ionization dynamics of helium droplets irradiated by intense, femtosecond extreme ultraviolet (XUV) pulses is investigated in detail by photoelectron spectroscopy. Helium droplets are resonantly excited to atomic-like 2p states with a photon energy of 21.5 eV and autoionize by interatomic Coulombic decay (ICD). A complex evolution of the electron spectra as a function of droplet size (250 to 10 6 He atoms per droplet) and XUV intensity (10 9 –10 12 W cm −2 ) is observed, ranging from narrow atomic-like peaks that are due to binary autoionization, to an unstructured feature characteristic of electron emission from a nanoplasma. The experimental results are analyzed and interpreted with the help of a numerical simulation based on rate equations taking into account all relevant processes—multi-step ionization, electronic relaxation, ICD, secondary inelastic collisions, desorption of electronically excited atoms, and collective autoionization (CAI).
Publisher: Optica Publishing Group
Date: 23-09-2020
DOI: 10.1364/OE.401249
Abstract: Collinear double-pulse seeding of the High-Gain Harmonic Generation (HGHG) process in a free-electron laser (FEL) is a promising approach to facilitate various coherent nonlinear spectroscopy schemes in the extreme ultraviolet (XUV) spectral range. However, in collinear arrangements using a single nonlinear medium, temporally overlapping seed pulses may introduce nonlinear mixing signals that compromise the experiment at short time delays. Here, we investigate these effects in detail by extending the analysis described in a recent publication (Wituschek et al., Nat. Commun., 11 , 883, 2020). High-order fringe-resolved autocorrelation and wave packet interferometry experiments at photon energies 23 eV are performed, accompanied by numerical simulations. It turns out that both the autocorrelation and the wave-packet interferometry data are very sensitive to saturation effects and can thus be used to characterize saturation in the HGHG process. Our results further imply that time-resolved spectroscopy experiments are feasible even for time delays smaller than the seed pulse duration.
Publisher: Springer Science and Business Media LLC
Date: 08-01-2020
DOI: 10.1038/S41467-019-13681-6
Abstract: The relaxation of photoexcited nanosystems is a fundamental process of light–matter interaction. Depending on the couplings of the internal degrees of freedom, relaxation can be ultrafast, converting electronic energy in a few fs, or slow, if the energy is trapped in a metastable state that decouples from its environment. Here, we study helium nanodroplets excited resonantly by femtosecond extreme-ultraviolet (XUV) pulses from a seeded free-electron laser. Despite their superfluid nature, we find that helium nanodroplets in the lowest electronically excited states undergo ultrafast relaxation. By comparing experimental photoelectron spectra with time-dependent density functional theory simulations, we unravel the full relaxation pathway: Following an ultrafast interband transition, a void nanometer-sized bubble forms around the localized excitation (He $${}^{* }$$ * ) within 1 ps. Subsequently, the bubble collapses and releases metastable He $${}^{* }$$ * at the droplet surface. This study highlights the high level of detail achievable in probing the photodynamics of nanosystems using tunable XUV pulses.
Publisher: IOP Publishing
Date: 13-11-2015
Publisher: American Physical Society (APS)
Date: 12-04-2021
Publisher: American Physical Society (APS)
Date: 19-01-2017
Publisher: IOP Publishing
Date: 13-08-2013
No related grants have been discovered for Paolo Piseri.