PERFORMANCE OF THE ASHURA KRF LASER AND ITS UPGRADING PLAN

Achieved performance of and the future plan for the ASHURA, a 700-J Kr F laser, are described. Nanosecond pulses (3-20 ns) with a bandwidth o f 50 cm-1 have been produced by gain switching of a preamplifier. The pulses have been six-time angularly multiplexed and double-pass amplif ied by two electron-beam-pumped amplifiers. The output from the main a mplifier is strongly saturated, and maximum energy of 660 J has been e xtracted in 90 ns with a stage gain of 40. Focused by an f = 1 m spher ical lens, maximum power density of 6 x 10(14) W/cm2 can be obtained o n target. The energy density ratio of prepulse on target has been supp ressed below 1/10(7). The ASHURA is being upgraded by adding a next-st age amplifier that aims at 10-kJ output energy in 270 ns.