Laser Mégajoule uses a series of 240 laser beamlines, grouped into eight groups of 30. Each beamline contains two main glass amplifiers, which are optically pumped using xenon flashlamps. A "feeder" laser beam is fed via optical fiber into each of the beamlines where it travels through the two amplifiers. In order to extract more power from the amplifiers, which are not particularly efficient in transmitting power to the beam, the laser pulse is sent through the amplifiers twice by an optical switch in front of a mirror. At the other end of the beamline a deformable mirror is used to remove imperfections in the wavefront.