Mixed metal dielectric pulse compression gratings

A Petawatt facility called PETAL (PETawatt Aquitaine Laser) is under development near the LIL (Ligne d'Integration Laser) at CEA Cesta, France. PETAL facility uses chirped pulse amplification (CPA) technique [1]. This system needs large pulse compression grating exhibiting damage threshold of more than 4 J/cm(2) normal beam at 1.053 mu m and for 500fs pulses. In this paper, we study an alternative design to the classic multilayer dielectric (MLD) grating [2] called "mixed metal-multilayer dielectric grating" (MMLD). This design consists in a gold reflective layer coated with a few pairs of HfO2/SiO2 [3]. The top low index SiO2 layer of the stack is then engraved to receive the grating. We evidenced in a previous work that leads to high efficient pulse compression gratings [3]. We have shown in last Boulder Damage Symposium that mixed mirror is equivalent to a "classic" MLD mirror [4]. We herein detail the damage performances obtained on the MMLD gratings and compare them with these of MLD gratings.