Performance of the ASHURA KrF laser and its upgrading plan

Abstract

Achieved performance of and the future plan for the ASHURA, a 700-J KrF laser, are described. Nanosecond pulses (3–20 ns) with a bandwidth of 50 cm -1 have been produced by gain switching of a preamplifier. The pulses have been six-time angularly multiplexed and double-pass amplified by two electron-beam-pumped amplifiers. The output from the main amplifier is strongly saturated, and maximum energy of 660 J has been extracted in 90 ns with a stage gain of 40. Focused by an f = 1m spherical lens, maximum power density of 6 × 10 14 W/cm 2 can be obtained on target. The energy density ratio of prepulse on target has been suppressed below 1/10 7 . The ASHURA is being upgraded by adding a next-stage amplifier that aims at 10-kJ output energy in 270 ns.