arXiv subjects

Fabrice Catoire

Publications and source records attributed to Fabrice Catoire.

6 recordsLinked to original sources

arXiv2026

High order harmonic Optical Reconstruction by delayed time-depeNdent Ellipticity perturbaTion: HORNET

We present and demonstrate an all-optical \textit{in situ} method for temporal characterisation of high-order harmonics generated in gas with a linearly polarised intense infrared (IR) laser. By using a delayed cross-polarised replica of the IR pulse with a lower amplitude, we introduce a weak and time-dependent ellipticity in the IR driving field. Since the XUV emission is very sensitive to the ellipticity of the driving field, it is perturbed precisely at the times when ellipticity is significant. The detected emission is then reduced only if the unperturbed XUV emission is substantial at these times. Perturbed XUV spectra are recorded for several delays and exhibit changes both in amplitude and in their spectral content. An iterative ptychographic algorithm is used to retrieve the electric field of individual harmonics in a very robust way. Experimental measurements are in good agreement with simulations. The reconstructed temporal profiles show a steady evolution of the XUV pulse duration and chirp with the harmonic order. The highest harmonics exhibit a positive chirp and are emitted in the rising front of the IR driving pulse, while the lowest ones exhibit a negative chirp and are emitted throughout the entire pulse.

physics.optics↗

arXiv2026

Floquet-engineering unveiled by high-harmonic generation

Ultrafast optical control of solids has uncovered new phenomena and advanced non-equilibrium condensed matter physics, where photon dressed electronic states - Floquet Bloch states (FBSs) - emerge under a strong oscillating laser field, also known as Floquet engineering. Although FBSs have been extensively investigated using time and angle resolved photoemission spectroscopy, direct evidence of their role in high-harmonic generation spectroscopy (HHGS) has remained elusive. Here, we present combined experimental and theoretical evidence that FBSs can be probed by HHG emission in the wide-bandgap solid magnesium oxide (MgO) driven by few cycle near infrared pulses. Experimentally, we observe clear evidence of FBSs in the HHG yield dependence on the crystal orientation. This specific feature is attributed to nonadiabatic coupling between FBSs and conduction bands near the Brillouin zone edge, where the strong laser field transiently breaks time reversal symmetry. We have confronted the experimental findings with numerical solutions of the time dependent Schrödinger equation, which reproduce the new feature and confirm its Floquet origin. The theoretical results show a coupling inducing a local band structure renormalization and Floquet like hybridization under strong field excitation. It also shows that FBS nonadiabatic dynamics persist in the strong field regime, establishing HHGS as a powerful probe of ultrafast light induced band hybridization in solids.

quant-ph↗

arXiv2026

Modular multiscale approach to modelling high-harmonic generation in gases

We present a modular user-oriented simulation toolbox for studying highharmonic generation in gases. The first release consists of the computational pipeline to 1) compute the unidirectional IR-pulse propagation incylindrical symmetry, 2) solve the microscopic responses in the whole macroscopic volume using a 1D-TDSE solver, 3) obtain the far-field harmonic field using a diffraction-integral approach. The code comes with interfaces and tutorials, based on practical laboratory conditions, to facilitate the usage and deployment of the code both locally and in HPC-clusters. Additionally, the modules are designed to work as stand-alone applications as well, e.g., 1D-TDSE is available through Pythonic interface.

physics.optics↗

arXiv2025

Harmonic Structure of the Brunel spectra

Electromagnetic emissions, known as Brunel radiations, are produced in plasmas through the coupling between the free electron density and ultrafast ionizing laser pulses. The radiation spectrum generated in laser-gas interactions is here investigated from a local current model for laser drivers with two frequency components - or "colors" - being not necessarily integers of one another. We provide a general description of this spectrum by deriving analytically the convolution product of the Fourier transforms of the electron density and of the laser electric field. Our analysis reveals that the only knowledge of the optical field extrema in time domain is sufficient to reproduce faithfully the numerically-computed Brunel spectrum and justify the emergence of various resonance frequencies. The classical combination of two laser harmonics, i.e., a fundamental and its second harmonic, is also addressed.

physics.optics↗

arXiv2023

Optical Probing of Ultrafast Laser-Induced Solid-to-Overdense-Plasma Transitions

Understanding the target dynamics during its interaction with a relativistic ultrashort laser pulse is a challenging fundamental multi-physics problem involving at least atomic and solid-state physics, plasma physics, and laser physics. Already, the properties of the so-called pre-plasma formed as the laser pulse's rising edge ionizes the target are complicated to access in experiments and modeling, and many aspects of this laser-induced transition from solid to overdense plasma over picosecond time scales are still open questions. At the same time, applications like laser-driven ion acceleration require precise knowledge and control of the pre-plasma because the efficiency of the acceleration process itself crucially depends on the target properties at the arrival of the relativistic intensity peak of the pulse. By capturing the dynamics of the initial stage of the interaction, we report on a detailed visualization of the pre-plasma formation and evolution. Nanometer-thin diamond-like carbon foils are shown to transition from solid to plasma during the laser rising edge with intensities < 10^16 W/cm^2. Single-shot near-infrared probe transmission measurements evidence sub-picosecond dynamics of an expanding plasma with densities above 10^23 cm^-3 (about 100 times the critical plasma density). The complementarity of a solid-state interaction model and a kinetic plasma description provides deep insight into the interplay of ionization, collisions, and expansion.

physics.plasm-ph↗

arXiv2016

Role of Excited States In High-order Harmonic Generation

We investigate the role of excited states in High-order Harmonic Generation by studying the spectral, spatial and temporal characteristics of the radiation produced near the ionization threshold of argon by few-cycle laser pulses. We show that the population of excited states can lead either to direct XUV emission through Free Induction Decay or to the generation of high-order harmonics through ionization from these states and recombination to the ground state. By using the attosecond lighthouse technique, we demonstrate that the high-harmonic emission from excited states is temporally delayed by a few femtoseconds compared to the usual harmonics, leading to a strong nonadiabatic spectral redshift.

physics.atom-ph↗