ABSTRACT
The Laser Megajoule (LMJ) is among the most energetic inertial confinement fusion laser facilities in the world, together with the National Ignition Facility (NIF) in the USA. The construction of the facility began back in 2003, and the first photons were emitted by the laser bundle #28 in 2014. Today, 11 laser bundles consisting of 88 large aperture 0.35×0.35m 2 laser beams are in operation, delivering daily up to 330 kJ of energy at the wavelength of 351 nm on a target placed in the center of a 10 m diameter vacuum chamber. In this paper, we describe the laser system and its operational performances. We also detail the first laser campaigns carried out to prepare an increase of energy and power on the target. These campaigns, along with the completion of additional bundles mounting, will bring LMJ performance to 1.3 MJ thanks to 22 bundles in operation.
ABSTRACT
The peak-power of petawatt-class lasers is limited by laser-induced damage to final optical components, especially on the pulse compression gratings. Multilayer dielectric (MLD) gratings are widely used in compressor systems because they exhibit a high diffraction efficiency and high damage threshold. It is now well established that the etching profile plays a key role in the electric field distribution, which influences the laser damage resistance of MLD gratings. However, less attention has been devoted to the influence of the multilayer design on the laser damage resistance of MLD gratings. In this Letter, we numerically and experimentally evidence the impact of the dielectric stack design on the electric field intensity (EFI) and the laser-induced damage threshold (LIDT). Three different MLD gratings are designed and manufactured to perform laser damage tests. On the basis of the expected EFIs and diffraction efficiencies, the measured LIDTs show how the multilayer design influences the laser resistance of the MLD gratings. This result highlights the impact of the multilayer dielectric design on the electric field distribution and shows how to further improve the laser-induced damage threshold of pulse compression gratings.
