Laboratoire pour l'utilisation des lasers intenses

The capabilities of the world's highest energy and peak-power pulsed lasers are limited by optical damage, and further advances in high-intensity laser science will require optics that are substantially more robust than existing components. We describe here the experimental demonstration of off-axis diffractive gaseous lenses capable of withstanding extreme laser fluence and immune to cumulative damage. We used less than 8 mJ of energy from interfering ultraviolet laser pulses to holographically write millimeter-scale diffractive gas lenses into an ozone, oxygen, and carbon-dioxide gas mixture. These lenses allowed us to focus, defocus, and collimate 532-nm nanosecond laser pulses with up to 210 mJ of energy at efficiencies above 50% and fluences up to 35 J/cm$^2$. We also show that the gas lenses have sufficient bandwidth to efficiently diffract 35-fs 800-nm pulses and that beam pointing, divergence, and diffraction efficiency are stable while operating at 10 Hz. These diffractive lenses are simple holograms, and the principles demonstrated here could be extended to other types of optics, suggesting that gaseous optics may enable arbitrary, damage-resistant manipulation of intense light for next-generation ultra-high-power lasers.

Spatial coherent beam combining (CBC) strategies are particularly promising for lasers dedicated to nuclear fusion applications for the purpose of developing high-energy and high-repetition-rate lasers. Let us examine their potential application to high-energy, large-size beams with repetition rates that preclude phase correlation between subsequent pulses. Both passive and active CBC approaches are investigated in this study to identify the most appropriate and effective strategy for large-aperture, high-energy laser amplifiers. Specific experiments have been conducted to validate promising architectures for lasers dedicated to inertial confinement fusion (ICF) applications. Based on these experimental results, examples of suitable and well-adapted setups are proposed.

Laser shock applications are numerous and various. They all require to know how pressure loading—due to laser irradiation—is influenced by laser parameters. This study aims at analyzing the influence of laser intensity distribution on pressure loading. This work presents the results from laser shots proceeded at LULI2000 on aluminum with LiF window targets. First, laser parameters are introduced and the radial distribution of laser intensity is estimated, thanks to a fourfold Gaussian distribution. Then, the experimental results and post-mortem samples are analyzed. Afterward, two methodologies to estimate the laser pressure loading—considering the laser intensity distribution—are described, applied, and compared. The first one with the monodimensional multi-physics simulation code ESTHER and the second one coupling the use of both ESTHER and the bidimensional (2D) hydrodynamics simulation code HESIONE [Aubert et al., J. Laser Appl. 31, 042014 (2019)]. The discussion presents the accuracy of these two methodologies regarding the experimental results. Comparison with a perfect top-hat laser intensity distribution highlights the edge effects. Finally, future possible works are suggested such as testing the methodology on other laser facilities or using a 2D/3D multi-physics simulation code.

A pioneering detailed comparative study of the dynamics of plasma flows generated by high-power nanosecond and high-intensity femtosecond laser pulses with similar fluences of up to 3×104 J/cm2 is presented. The experiments were conducted on the petawatt laser facility PEARL using two types of high-power laser radiation: femtosecond pulses with energy exceeding 10 J and a duration less than 60 fs, and nanosecond pulses with energy exceeding 10 J and a duration on the order of 1 ns. In the experiments, high-velocity (>100 km/s) flows of «femtosecond» (created by femtosecond laser pulses) and «nanosecond» plasmas propagated in a vacuum across a uniform magnetic field with a strength over 14 T. A significant difference in the dynamics of «femtosecond» and «nanosecond» plasma flows was observed: (i) The «femtosecond» plasma initially propagated in a vacuum (no B-field) as a collimated flow, while the «nanosecond» flow diverged. (ii) The «nanosecond» plasma interacting with external magnetic field formed a quasi-spherical cavity with Rayleigh–Taylor instability flutes. In the case of «femtosecond» plasma, such flutes were not observed, and the flow was immediately redirected into a narrow plasma sheet (or «tongue») propagating across the magnetic field at an approximately constant velocity. (iii) Elongated «nanosecond» and «femtosecond» plasma slabs interacting with a transverse magnetic field broke up into Rayleigh–Taylor «tongues». (iv) The ends of these «tongues» in the femtosecond case twisted into vortex structures aligned with the ion motion in the external magnetic field, whereas the «tongues» in the nanosecond case were randomly oriented. It was suggested that the twisting of femtosecond «tongues» is related to Hall effects. The experimental results are complemented by and consistent with numerical 3D magnetohydrodynamic simulations. The potential applications of these findings for astrophysical objects, such as short bursts in active galactic nuclei, are discussed.

We report the observation of Zeeman splitting in multiple spectral lines emitted by a laser-produced, magnetized plasma (1–3 × 1018 cm−3, 1–15 eV) in the context of a laboratory astrophysics experiment under a controlled magnetic field up to 20 T. Nitrogen lines (NII) in the visible range (563–574 nm) were used to diagnose the magnetic field and plasma conditions. This was performed by coupling our data with the Stark–Zeeman line-shape code PPPB. The excellent agreement between experiment and simulations paves the way for a non-intrusive experimental platform to get time-resolved measurements of the local magnetic field in laboratory plasmas.

Apollon est une infrastructure laser d’Ultra-Haute Intensité fournissant des impulsions multi-PW pour la recherche en interaction laser-matière et physique des plasmas. Ouverte aux utilisateurs depuis 2021, elle comporte deux zones : SFA pour les interactions à très haute intensité et l’accélération d’ions, et LFA pour l’accélération d’électrons. Apollon a déjà dépassé 10 22 W/cm 2 et poursuit sa montée en puissance vers de nouveaux régimes QED.

Plasma filaments in the air are generated using a coherently combined ultrashort fiber laser, reaching the highest repetition rate of 333 kHz reported to date. Cumulative effects of pulse burst on the filament length and longitudinal shift are investigated.

We report on a versatile coherently combined ultrashort fiber laser allowing an independent peak and average power adjustment, pulse-on-demand, and repetition rate management, needed for laser-matter interaction applications.