Beam control and power conditioning of GEKKO glass laser system

The glass laser fusion driver, GEKKO 12 beam system, at ILE, Osaka can be operated since 1983 to deliver 20 kJ output in 1 ns pulse with the second and third harmonic frequency converters and the pulse tailoring optics. The uniform irradiation of the spherical target in the implosion experiments is a key issue to get the higher density of final compressed core. The pulse power to drive 2000 flash lamps exciting the rod and disk amplifiers is a moderate system with the total energy of 21 MJ in 300 μs duration. High reliability and reproducibility are required to keep the laser energy balance of 12 beams within 3%, and no misfiring 88 high voltage switches of the laser amplifiers and 14 Pockels optical switches with the total probability less than 0.1% per shot. Power balance technology involves not only the power conditioning of the flash power supply but also the gain control of the amplifiers and the alignment of a phase angle of the frequency converters, both working very nonlinearly. The precise control is sustained by the precise measurements of the beam energies, power waveforms, and the optical components characteristics such as reflectivity and transmittance. This paper includes the optical beam control to realize the uniform illumination with an incoherent light source and the optical phase control in a focusing optics