The Laser Megajoule (LMJ) is a high energy laser facility under construction in Bordeaux for the French nuclear research agency (Commissariat à l'Energie Atomique, CEA). At completion, 240 pulsed laser beams will be focused on a 2 mm target, delivering 2 MJ and producing the high density, pressure and temperature conditions where nuclear fusion triggers.

An original feature of the LMJ is the use of large diffractive optic components, where the only comparable system in the world (the American National Ignition Facility at Lawrence Livermore Laboratories in California) uses classical dioptric components.

Thanks to a close cooperation between CEA and HORIBA Jobin Yvon scientists, the feasibility of these unique components (400×400 mm focusing gratings) was confirmed and production started in 2000 for the demonstration prototype which confirmed the high performance of the design.

The profile figure presents the SEM profile of the gratings produced at HORIBA Jobin Yvon: the groove depth is 2 times the period which was a real challenge. The uniformity over the 420x470 mm surface is also a technological achievement.