Design principle and first results obtained on the LMJ deformable mirror prototype

The laser Megajoule (LMJ) project was launched in 1995 by the French Atomic Energy Commission and is aimed at developing a facility to achieve inertial confinement fusion. The LMJ architecture is based on 240 laser beamlines to be focused onto a millimetre size target. To meet this challenge, one of the main issues consists in a proper control of the quality of the beam wavefront at the output of the laser. For this purpose, the LMJ makes use of a large-size adaptive mirror (named M1 in the actual laser baseline), with 400 by 400 mm(2) useful aperture. This paper provides an overview of the M1 prototype, using 39 mechanical actuators. This mirror was made by the French company CILAS (c) together with the help of ISP (c) for the mechanical actuators. CEA, Cilas and ISP have joined their efforts to complete the overall design. The prototype has been tested on the Laser Integration Line (LIL). This facility is fully consistent with the LMJ requirements, a complete laser chain which comprises 4 beamlines. After presenting the basic design principles, we focus on the demonstrated performance measured on a dedicated setup, as well as on LIL facility.