arXiv subjects

Franck Lépine

Publications and source records attributed to Franck Lépine.

8 recordsLinked to original sources

arXiv2026

Tailoring Attosecond Charge Migration in Native Molecular Ions

Attosecond chemistry involves developing strategies to manipulate electronic coherent waves in molecules, which can influence the outcome of photoinduced reactions. While recent progress in this field calls for investigations of increasingly complex isolated or embedded systems, theoretical predictions on attosecond charge migration have remained limited to native neutral species. Since molecules in nature often carry a native charge, there is potential biological and chemical interest in determining whether attosecond charge migration is affected by an additional charge. In this study, we employ high-level correlated methods to study purely electronic dynamics induced by hole-mixing in molecular ions. Our results, obtained for a series of neutral, protonated and deprotonated molecules, reveal that the likelihood of observing attosecond electron dynamics can either be degraded or improved by the presence of an initial charge, and that the existence of the dynamics is correlated with the strength of electron correlation. These findings will stimulate further experimental and theoretical investigations into this unexplored field of attosecond dynamics in molecular ions.

physics.chem-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

Femtosecond Nonadiabatic Confinement of Molecular Dication Yield

Doubly charged molecular cations often carry signatures of electronic correlation and electron-nuclear entanglement present in the parent cation. Here, we produce ethylene dications using a combination of an extreme ultraviolet pump and near-infrared probe pulses, observing a peak in the dication yield at a pump-probe delay of approximately 15 fs. Ab-initio calculations, which explicitly take into account coupled electron-nuclear dynamics induced by the pump and the multiphoton nature of the probe-induced ionization step, reproduced the observed delay in the yield. It originates from resonant enhancement of the multiphoton ionization of the electronically excited ethylene cation as the carbon-carbon double bond expands. However, this effect is tempered by rapid nonadiabatic relaxation of the excited ionic states. Our results suggest a general mechanism whereby ultrafast nonadiabatic relaxation of a molecular ion can compete with its strong-field ionization rate, confining the dication yield to a narrow temporal window of a few femtoseconds.

physics.chem-ph↗

arXiv2025

Ultrafast probing of isotope-induced explciit symmetry breaking in ethylene

Symmetry governs nature's law, yet many of the natural phenomena occur due to the breakdown of symmetry. Here, we show how isotope-induced inversion symmetry breaking influences ultrafast photoisomerization processes in ethylene. Using extreme ultraviolet pump-near infrared probe time-of-flight mass spectrometry, we find that replacing one of the carbon atoms in ethylene with a 13C isotope leads to twice-faster structural relaxation via ethylene-ethylidene isomerization in the photo-excited molecular cation. Advanced trajectory surface hopping calculations incorporating the nuclear symmetry of the molecular systems, reveal that it arises from the mixing of different normal modes in the isotope-substituted species, interactions otherwise forbidden by symmetry. Although the mixing does not alter the symmetry of the electronic Hamiltonian, it modifies that of the nuclear Hamiltonian, causing explicit symmetry breaking. This facilitates efficient intra-molecular vibrational energy redistribution, lowering the isomerization yield. Our findings offer opportunities to use isotope-induced nuclear symmetry breaking to control the outcome of light-molecule interactions across ultrafast timescales.

physics.chem-ph↗

arXiv2024

Angular momentum dependence in multiphoton ionization and attosecond time delays

Attosecond ionization time-delays at photoelectron energies above typically 10 eV are usually interpreted using the so called asymptotic approximation as a sum of the atomic or molecular delays with a universal laser-induced contribution. Here, we employ a two-harmonic RABITT (Reconstruction of Attosecond Beating by Interference of Two-photon Transitions) configuration to isolate the multiphoton pathways and measure the ionization time delays as a function of the dressing field intensity. We show that the validity of the asymptotic theory can be extended to the threshold or to higher-order contributions by rigorously treating the angular-momentum dependence of the continuum-continuum transitions into universal and easily computable partial-wave-specific correction factors. Our asymptotic treatment is also valid for higher-order interfering amplitudes while significantly simplifying their evaluation and providing a transparent physical interpretation. The validity of the method for atomic and molecular targets in the vicinity of resonances, ionization thresholds, and for both the emission-integrated and angularly resolved signal is confirmed by comparison to ab initio calculations over a wide energy range.

physics.atom-ph↗

arXiv2024

THz to far-infrared spectra of the known crystal polymorphs of Phenylalanine

There is renewed interest in the structure of the essential amino acid Phenylalanine in the solid state. Three new polymorphs were found in the years 2012 to 2014. Here, we investigate the structure, stability, and energetical ordering of these phases using first-principles simulations at the level of Density Functional Theory incorporating van-der-Waals interactions. Two of the distinct crystal forms are found to be structurally similar and energetically very close after vibrational free energy corrections have been taken into account. Infrared absorption spectra are likewise calculated and compared to experimental measurements. By combining measurements obtained with a commercial Fourier Transform Infra-Red spectrometer and a homemade air-photonics-based THz Time Domain spectrometer, we could carry out this comparison in the vibrational frequency region from 1 to 40~THz. The excellent agreement of the line positions and the established energy ranking allow us to identify the most stable polymorph of Phenylalanine.

physics.chem-ph↗

arXiv2023

Condensed Matter Systems Exposed to Radiation: Multiscale Theory, Simulations, and Experiment

This paper reviews the new highly interdisciplinary research field studying the behavior of condensed matter systems exposed to radiation. The paper highlights several relevant examples of recent advances in the field and provides a roadmap for the development of the field in the next decade. Condensed matter systems exposed to radiation may have very different natures, being inorganic, organic or biological, finite or infinite, be composed of many different molecular species or materials, existing in different phases (solid, liquid, gaseous or plasma) and operating under different thermodynamic conditions. The essential and novel element of this research is that, despite the vast diversity of such systems, many of the key phenomena related to the behavior of irradiated systems (such as radiation-induced damage, mechanisms of damage repair and control, radiation protection, etc.) are very similar and can be understood based on the same fundamental theoretical principles and computational approaches. One of the essential features of the aforementioned phenomena concerns their multiscale nature as the manifestation of the radiation-induced effects occurring at different spatial and temporal scales ranging from the atomic to the macroscopic. The multiscale nature of the effects and similarity of their manifestation in systems of different origins necessarily brings together different disciplines, such as physics, chemistry, biology, materials and nano-science, and biomedical research, demonstrating numerous interlinks and commonalities between them. This research field is highly relevant to many novel and emerging technologies and medical applications.

physics.chem-ph↗

arXiv2021

Anisotropic dynamics of two-photon ionization: An attosecond movie of photoemission

Imaging in real time the complete dynamics of a process as fundamental as photoemission has long been out of reach due to the difficulty of combining attosecond temporal resolution with fine spectral and angular resolutions. Here, we achieve full decoding of the intricate angle-dependent dynamics of a photoemission process in helium, spectrally and anisotropically structured by twophoton transitions through intermediate bound states. Using spectrally- and angularly-resolved attosecond electron interferometry, we characterize the complex-valued transition probability amplitude towards the photoelectron quantum state. This allows reconstructing in space, time and energy the complete formation of the photoionized wavepacket.

physics.atom-ph↗