Design, optimization and development of pulse compression gratings for the MPW-HE LIL

The french Commissariat l'Energie Atomique (CEA) develops a multipetawatt laser in the Laser Integration Line (LIL), prototype of the future Megajoule Laser [1]. This Petawatt laser line will deliver impulsions of 7.2 PW, 500 fs at the wavelength of 1053 nm. The chirped pulse amplification (CPA) method is used [2]. We work on the modelization and the fabrication of gratings used in the CPA scheme. Since damage threshold of more than 3 J/cm(2) @ 500fs are needed, we retained multidielectric gratings (MLD) instead of classical gold gratings. These gratings, developed in mid 90's, consist in a multidielectric mirror stack with its top layer engraved with a grating structure. We have been working to optimize the groove geometry of the MLD grating to minimize the E field maximum in the structure. An innovative design using a mixed metal/dielectric mirror stack was also studied. The scope of this paper is to present our main numerical results in these different domains.