Asterix IV/PALS is a single-beam laser system. It consists of an oscillator section that generates the initial pulse, followed by a succession of five power amplifiers in which the pulse is boosted to a high energy. This arrangement is called master oscillator power amplifier (MOPA). The size of the amplifiers gradually increases along the chain, and the beam diameter is increased from the initial 3 mm at the output of the oscillator to 290 mm at the output of the final amplifier. The beam expansion is achieved in spatial filters regularly placed between the amplifiers. The Faraday rotator prevents the light reflected from the target from counter-propagating the chain and damaging the initial stages of the system.
In addition to the 290 mm main beam, the laser delivers a 148 mm auxiliary beam obtained by splitting off a fraction of the A4 amplifier using a semi-transparent mirror. It can be separately synchronized to the main pulse and can be employed for instance to drive backlighter or prepulse plasmas.