Mixed metal dielectric gratings for pulse compression applications

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 gratings exhibiting damage threshold of more than 4 J/cm2 beam normal at 1.053μm and for 500fs pulses. In this paper, we study an alternative design to the classic Multidielectric (MLD) gratings [2] called "mixed metal-multidielectric grating" (MMLD). In this design, the dielectric mirror stack of the MLD grating is replaced by a gold reflective layer covered with a few pairs of HfO2/SiO2 [3]. The number of pairs must be high enough to ensure a sufficient reflection coefficient in order to prevent damage of the gold layer. On the top of the stack, a silica layer is coated to receive the grating. After some considerations on the grating design and optimization, a comparison between MLD and MMLD mirrors is also carried out. We finally detail the measured diffraction efficiencies obtained on MMLD gratings.

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