arXiv subjects

Jérémy R. Rouxel

Publications and source records attributed to Jérémy R. Rouxel.

9 recordsLinked to original sources

arXiv2026

X-ray diffraction from chiral molecules with twisted beams

Structured x-rays carrying an orbital angular momentum break spatial inversion symmetry and have been proposed as probes of chirality. We theoretically investigate twisted non-resonant x-ray diffraction from chiral molecules and demonstrate that no dichroic signal can arise from randomly oriented molecules, irrespective of the beam spatial profile. However, a dichroic response emerges for oriented molecules. Our results establish the beam and sample conditions for which a measurable dichroic scattering signal survives axial and focal averaging.

physics.optics↗

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↗

arXiv2025

Linear and nonlinear X-ray spectra of chiral molecules: X-ray Circular Dichroism, Sum- and Difference-Frequency Generation of fenchone and cysteine

Recent advancements in X-ray light sources at synchrotrons and X-ray free-electron lasers (XFELs) present exciting opportunities to probe molecular chirality using novel nonlinear spectroscopies with element-sensitivity. Circular dichroism (CD) and sum- and difference-frequency generation (SFG/DFG) are established techniques for probing molecular asymmetry in optical regime, with SFG/DFG offering unique advantages due to their background-free nature and independence from circularly polarized light sources. Extending them into the X-ray domain provides deeper insights into local structural asymmetries by leveraging the localized nature of core orbitals. In this work, we simulate X-ray absorption spectroscopy (XAS), X-ray circular dichroism (XCD) and nonlinear optical/X-ray SFG and DFG (OX SFG/DFG) signals for two prototypical chiral molecules, fenchone and cysteine. Our multi-reference simulations reproduce experimental data when available and reveal how novel X-ray spectroscopies exploit the site- and element-sensitivity of X-rays to uncover molecular asymmetry. The XCD spectra show strong asymmetries at chiral centers, while distant atoms contribute less. The OX SFG/DFG signals, under fixed resonant optical excitation, strongly depend on core transition and valence excitation energies. This dependence allows us to introduce two-dimensional (2D) chirality-sensitive valence-core spectroscopy, which provides insight into the overlap between valence orbitals and local molecular asymmetry. Finally, our estimates using realistic laser and X-ray pulse parameters demonstrate that such nonlinear experiments are feasible at XFELs, offering a promising tool for investigating the geometric and electronic structures of chiral molecules.

physics.chem-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↗

arXiv2020

Chiral Four-Wave-Mixing signals with circularly-polarized X-ray pulses

Chiral four-wave-mixing signals are calculated using the irreducible tensor formalism. Different polarization and crossing angle configurations allow to single out the magnetic dipole and the electric quadrupole interactions. Other configurations can reveal that the chiral interaction occurs at a given step within the nonlinear interaction pathways contributing to the signal. Applications are made to the study of valence excitations of S-ibuprofen by chiral Stimulated X-ray Raman signals at the Carbon K-edge and by chiral visible 2D Electronic Spectroscopy.teraction pathways contributing to the signal.

physics.chem-ph↗

arXiv2019

Monitoring Spontaneous Charge-density Fluctuations by Single-molecule Diffraction of Quantum Light

Homodyne X-ray diffraction signals produced by classical light and classical detectors are given by the modulus square of the charge density in momentum space $\left|σ(\mathbf{q})\right|^{2}$, missing its phase which is required in order to invert the signal to real space. We show that quantum detection of the radiation field yields a linear diffraction pattern that reveals $σ(\mathbf{q})$ itself, including the phase. We further show that repeated diffraction measurements with variable delays constitute a novel multidimensional measure of spontaneous charge-density fluctuations. Classical diffraction, in contrast, only reveals a subclass of even-order correlation functions. Simulations of two dimensional signals obtained by two diffraction events are presented for the amino acid cysteine.

physics.chem-ph↗

arXiv2018

X-Ray sum frequency generation; direct imaging of ultrafast electron dynamics

X-ray diffraction from molecules in the ground state produces an image of their charge density, and time-resolved X-ray diffraction can thus monitor the motion of the nuclei. However, the density change of excited valence electrons upon optical excitation can barely be monitored with regular diffraction techniques due to the overwhelming background contribution of the core electrons. We present a nonlinear X-ray technique made possible by novel free electron laser sources, which provides a spatial electron density image of valence electron excitations. The technique, sum frequency generation carried out with a visible pump and a broadband X-ray diffraction pulse, yields snapshots of the transition charge densities, which represent the electron density variations upon optical excitation. The technique is illustrated by ab initio simulations of transition charge density imaging for the optically induced electronic dynamics in a donor/acceptor substituted stilbene.

physics.chem-ph↗

arXiv2016

Photoinduced molecular chirality probed by ultrafast resonant X-ray spectroscopy

Recently developed circularly polarized X-ray light sources can probe ultrafast chiral electronic and nuclear dynamics through spatially localized resonant core transitions. We present simulations of time-resolved circular dichroism (TRCD) signals given by the difference of left and right circularly polarized X-ray probe transmission following an excitation by a circularly polarized optical pump with variable time delay. Application is made to formamide which is achiral in the ground state and assumes two chiral geometries upon optical excitation to the first valence excited state. Probes resonant with various K-edges (C, N and O) provide different local windows onto the parity breaking geometry change thus revealing enantiomer asymmetry.

physics.chem-ph↗

arXiv2016

Monitoring Nonadiabatic Electron-Nuclear Dynamics in Molecules by Attosecond Streaking of Photoelectrons

Streaking of photoelectrons has long been used for the temporal characterization of attosecond extreme ultraviolet pulses. When the time-resolved photoelectrons originate from a coherent superposition of electronic states, they carry an additional phase information, which can be retrieved by the streaking technique. In this contribution we extend the streaking formalism to include coupled electron and nuclear dynamics in molecules as well as initial coherences and demonstrate how it offers a novel tool to monitor non-adiabatic dynamics as it occurs in the vicinity of conical intersections and avoided crossings. Streaking can enhance the time resolution and provide direct signatures of electronic coherences, which affect many primary photochemical and biological events.

physics.chem-ph↗