Full-scale optic designed for onsite study of damage growth at the Laser MegaJoule facility.

Large fusion scale laser facilities aim at delivering megajoules laser energy in the UV spectrum and nanosecond regime. Due to the extreme laser energies, the laser damage of final optics of such beamlines is an important issue that must be addressed. Once a damage site initiates, it grows at each laser shot which decreases the quality of the optical component and spoil laser performances. Operation at full energy and power of such laser facilities requires a perfect control of damage kinetics and laser parameters. Monitoring damage kinetics involves onsite observation, understanding of damage growth process and prediction of growth features. Facilities are equipped with cameras dedicated to the monitoring of damage site growth. Here we propose to design and manufacture a dedicated full size optical component to study damage growth at increased energy, on the beamline, i.e. in the real environment of the optics on a large laser facility. Used for the first time in 2021, the growth statistics acquired by this approach at the Laser MegaJoule (LMJ) facility provides a new calibration point at a fluence less than 5 J cm-2 and a flat-in-time pulse of 3 ns.

Large optics metrology for high-power lasers.

The Laser MégaJoule (LMJ) is a high-power laser dedicated to laser-plasma experiments. At the beginning of the project in the mid-1990s, an optical metrology laboratory was created at CEA to help accomplish all the steps in the construction of this laser. This paper proposes an overview of the capabilities of this metrology laboratory in four main fields: surface imperfections, photometry, laser damage measurement, and wavefront measurement. The specificities for high-power laser optics in each domain are highlighted as well as the specific features that make our instruments unique.