Optical diagnostic technology of fusion laser system

As the lasers for nuclear fusion research, the construction of high power glass lasers has been rapidly carried out since 1970s. Around 1985, the glass laser of 100 kJ and 100 TW appeared, thus the remarkable technical development has been made. In the institute of Laser Engineering, Osaka University, a multi-beam system Gekko No.2 was installed in 1975 for the first time in Japan, and through a phosphate glass system Gekko No.4 as the first in the world, and Gekko M2 as the prototype of Gekko No.12, in 1983, Gekko No.12 of 20 kJ was completed. These laser systems are still in operation now. From November, 1983, high power amplifying test and target irradiation test were begun by using the Gekko No.12. In December, 1983, the largest output in the world of 57 TW was attained, and in the target implosion test, 4 x 1010 neutrons were generated, which was the largest in the world at that time. Thereafter, the automatic operation of the laser, laser wave form correction, the adoption of high endurance, no reflection elements and the second higher harmonic wave conversion using a single crystal KDP of 38 cm diameter, the largest in the world, were carried out, and those enabled the supply of 0.53 μm light at the maximum conversion efficiency of 86 %. The constitution of measuring instruments for Gekko No.12, the measuring techniques at the oscillator and the laser system are described. (Kako, J.)