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By using numerical simulations and experimental campaigns on a small-scale laser facility, the concept of the focal spot imaging on harmonics of laser frequency is developed and implemented on the Laser MegaJoule (LMJ)/PETawatt Aquitaine Laser (PETAL) facility. The Two/Three ω Imaging System was activated and validated during the first 2017–2019 interaction campaigns of PETAL on the LMJ. It provides major information on focal spot characteristics on a target. Such an approach could be easily applied to any high-intensity facility in the relativistic intensity regime (>1018 W cm−2). [ABSTRACT FROM AUTHOR]

Studies the propagation of a high-contrast frequency-doubled subpicosecond relativistic laser pulse through thin and initially solid foils. Correlation of the strong density threshold observed for the transmitted energy with clear modifications of the transmitted and reflected spectra, electron generation, and beam imaging.

Studies the propagation of a high-contrast subpicosecond laser pulse through long preformed overdense plasmas. Measurement of transmission values in plasmas; Comparison of results with one-dimensional analytical calculations of the hole boring effect; Effect of ponderomotive force.

Measurements of self-channeling of picosecond laser pulses due to relativistic and ponderomotive expulsion effects have been obtained in preformed plasmas at laser irradiances between 5-9 ×1018 Wcm-2. The self-focused channel was surrounded by a multi-megagauss magnetic field. The orientation of the field was consistent with a forward going relativistic electron beam propagating along the laser pulse. Self-channeling and magnetic field generation mechanisms were modeled by multidimensional particle-in-cell (PIC) simulations and good agreement was obtained with the experimental observations. Measurements of the channel expansion after the interaction were obtained and the rate of expansion was consistent with a blast wave solution. The level of transmission of an intense laser pulse through such performed density channels was observed to increase significantly compared to the case without a channel. High levels of transmission of an intense laser pulse through microtubes were also observed. The relevance of these results to the fast ignitor is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The first experiments on the National Ignition Facility (NIF) in the US started and will be followed by the Laser MégaJoule (LMJ) in France. Such facilities will provide unique tools for inertial confinement fusion (ICF) physics & for basic science. A petawatt short pulse laser (ps) is being added to the ns pulse beams of the LMJ. This is PETAL (PETawatt Aquitaine Laser), under construction on the LMJ site near Bordeaux (France). The Petal+ project is aiming at the design and construction of diagnostics dedicated to experiments with PETAL and LMJ laser beams. Within Petal+, three types of diagnostics are under study: a proton spectrometer, an electron spectrometer and a large-band X-ray spectrometer. The first goal of these diagnostics will be to characterize the secondary radiation and particle sources produced with PETAL. They will also be used for experiments using both ns and ps beams. In the present paper emphasis is put on the charged-particle diagnostics. [Copyright &y& Elsevier]

Ultrahigh power laser pulses delivered by the Alisé beamline (26 J, 32 TW pulses) have been sent vertically into the atmosphere. The highly nonlinear propagation of the beam in the air gives rise to more than 400 self-guided filaments. This extremely powerful bundle of laser filaments generates a supercontinuum propagating up to the stratosphere, beyond 20 km. This constitutes the highest power “atmospheric white-light laser” to date. [ABSTRACT FROM AUTHOR]