arXiv subjects

Gianluca Aldo Geloni

Publications and source records attributed to Gianluca Aldo Geloni.

5 recordsLinked to original sources

arXiv2026

Probing the Linewidth of the 12.4-keV $^{45}$Sc Isomeric Resonance in Solids by Nuclear Forward Scattering

The $^{45}$Sc transition from the nuclear ground state to the 12.389-keV isomer (lifetime 0.46~s) has an ultranarrow natural linewidth $Γ_{\ind{0}}\simeq 1.4$~feV, corresponding to a quality factor $\simeq 10^{19}$. This makes $^{45}$Sc a compelling candidate for nuclear-clock metrology, provided that coherence in solids can be maintained close to the natural limit. Here we investigate the linewidth and coherence properties of the $^{45}$Sc resonance in solids following resonant x-ray pumping. Using the European XFEL, we confirm persistence of the long-lived isomer excitation in a solid-state environment via time-delayed incoherent $K_{α,β}$ emission and observe a weak delayed elastic channel at 12.4~keV, from which we extract a partial internal-conversion coefficient $α_{K}=390(60)$. Time-domain nuclear forward scattering measurements in crystals of Sc, Sc$_2$O$_3$, ScN and ScAlMgO$_4$ at 20~K show no statistically significant coherent forward-scattering signal beyond $2$~ms; within the adopted linewidth-broadening model, we infer an effective broadening $ΔΓ\gtrsim 500\,Γ_{\ind{0}}$. These results provide the quantitative constraints on linewidth broadening in solid-state $^{45}$Sc with an intrinsic natural linewidth in the femto-electronvolt range thereby laying the groundwork for precision metrology in the X-ray regime and future nuclear-clock frequency references using $^{45}$Sc nuclear isomer.

quant-ph↗

arXiv2026

Roadmap on Attosecond Science

Twenty-five years have passed since the first experimental demonstration of attosecond pulses, marking the advent of our ability to resolve and control electron motion in real time. What began as a technological breakthrough - generating the shortest flashes ever produced - has evolved into a powerful approach for probing and steering electronic dynamics in atoms, molecules, and solids. This roadmap, authored by leading experts in the field, surveys the recent rapid progress in the generation and characterization of attosecond pulses, emerging attosecond measurement and control techniques, and their expanding range of applications. It reviews current and future developments in attosecond light sources, including novel laser technologies, waveform synthesizers, new schemes for high-order harmonic generation, attosecond pulse generation at free-electron lasers, and structured light. Advances in attosecond measurement methodologies are also discussed, encompassing all-attosecond pump-probe spectroscopy, attosecond four-wave mixing, attosecond microscopy, spectroscopy with light transients, and attosecond interferometry. Furthermore, the roadmap addresses applications of attosecond spectroscopy to reveal electron dynamics in molecules and condensed matter systems from both theoretical and experimental perspectives, and highlights emerging directions at the interface with quantum optics and quantum entanglement. Overall, this work aims to serve as a comprehensive resource for navigating the evolving landscape of attosecond science.

physics.optics↗

arXiv2026

Single-shot sorting of Mössbauer time-domain data at X-ray free-electron lasers

Mössbauer spectroscopy is widely used to study structure and dynamics of matter with remarkably high energy resolution, provided by the narrow nuclear resonance line widths. However, the narrow width implies low count rates, such that experiments commonly average over extended measurement times or many x-ray pulses (``shots''). This averaging impedes the study of non-equilibrium phenomena. It has been suggested that X-ray free-electron lasers (XFELs) could enable Mössbauer single-shot measurements without averaging, and a proof-of-principle demonstration has been reported. However, so far, only a tiny fraction of all shots resulted in signal-photon numbers which are sufficiently high for a single-shot analysis. Here, we demonstrate coherent nuclear-forward-scattering of self-seeded XFEL radiation, with up to 900 signal-photons per shot. We develop a sorting approach which allows us to include all data on a single-shot level, independent of the signal content of the individual shots. It utilizes the presence of different dynamics classes, i.e. different nuclear evolutions after each excitation. Each shot is assigned to one of the classes, which can then be analyzed separately. Our approach determines the classes from the data without requiring theory modeling nor prior knowledge on the dynamics, making it also applicable to unknown phenomena. We envision that our approach opens up new grounds for Mössbauer science, enabling the study of out-of-equilibrium transient dynamics of the nuclei or their environment.

quant-ph↗

arXiv2023

Opportunities for Gas-Phase Science at Short-Wavelength Free-Electron Lasers with Undulator-Based Polarization Control

Free-electron lasers (FELs) are the world's most brilliant light sources with rapidly evolving technological capabilities in terms of ultrabright and ultrashort pulses over a large range of accessible photon energies. Their revolutionary and innovative developments have opened new fields of science regarding nonlinear light-matter interaction, the investigation of ultrafast processes from specific observer sites, and approaches to imaging matter with atomic resolution. A core aspect of FEL science is the study of isolated and prototypical systems in the gas phase with the possibility of addressing well-defined electronic transitions or particular atomic sites in molecules. Notably for polarization-controlled short-wavelength FELs, the gas phase offers new avenues for investigations of nonlinear and ultrafast phenomena in spin orientated systems, for decoding the function of the chiral building blocks of life as well as steering reactions and particle emission dynamics in otherwise inaccessible ways. This roadmap comprises descriptions of technological capabilities of facilities worldwide, innovative diagnostics and instrumentation, as well as recent scientific highlights, novel methodology and mathematical modeling. The experimental and theoretical landscape of using polarization controllable FELs for dichroic light-matter interaction in the gas phase will be discussed and comprehensively outlined to stimulate and strengthen global collaborative efforts of all disciplines.

physics.atom-ph↗

arXiv2023

Towards the use of X-ray Free-Electron Laser electron beams to study Quantum Chromo-Dynamics

X-ray free-electron lasers (XFELs) utilize high-density and high-energy electron bunches which are well-suited to produce Compton back-scattering radiation. Here we study back-scattered radiation pulses produced by the interaction of XFEL electron beams and an optical laser. We discuss cost-effective setups to study such processes, taking advantage of the existing conventional as well as proposed XFEL infrastructure. We estimate parameters of possible experiments and compare them with other projects under construction.

physics.acc-ph↗