Frequency conversion for powerful lasers

The process of frequency conversion allows us to modify the wavelength of a laser beam. The interest of this modification comes from the fact that the shorter wavelength the more efficient the laser-plasma is coupling. In this paper, we present the part taken by the frequency conversion in the use of powerful lasers at CEA - Limeil-Valenton. After a short overview, we present the physical designs which are the basis of the laser frequency conversion. Finally, we describe the device planned for the Laser Megajoule to pass from the infrared wavelength to the required ultraviolet. The aim is to achieve a peak performance of 80 % and average performance better that 55 %. (authors)