Proceedings of International Conference on Physics in ... - KEK

CURRENT STATUS OF LFEX LASER AND EXA-WATT LASER CONCEPT
AT ILE/OSAKA
J. Kawanaka, LFEX-Team, EXA-Team, and H. Azechi
Institute for Laser Engineering, Osaka University, Yamadaoka, Suita 565-0871 Japan
Abstract
The LFEX laser has been developed for the basic
research <strong>of</strong> plasma heating in fast ignition scheme.
Its demonstration ensures the high potential <strong>of</strong> the LFEX
laser and various novel application fields has been
strongly discussed, such as lab-astrophysics, particle
physics and so on. We are planning the “Gekko-EXA”
laser, which is a sub-exa-watt ultrahigh peak power laser
where various advanced laser technologies developed in
the LFEX laser project are used. In this letter, the recent
status <strong>of</strong> the LFEX laser and the rough conceptual design
<strong>of</strong> “Gekko-EXA” are mentioned.
INTRODUCTION
The central ignition for the laser fusion has been
studied. The National Ignition Facility (NIF) in Lawrence
Liver More National Laboratory (LLNL) will
demonstrate it with a mega-joules class laser [1]. On the
other hand, the fast-ignition has been actively researched
in our institute. It reduces a total laser power to one tenth,
which improves not only a compactness <strong>of</strong> the laser
system but also a repeatability <strong>of</strong> laser operation and a
stability <strong>of</strong> the laser operation. A high peak power laser
with short pulse duration is necessary as a heating laser
for the fast ignition. The LFEX (Laser for Fusion
EXperiments)-Laser system has been developed to clarify
the heating mechanism [2]. The plasma heating
experiments have started by using the LFEX-Laser. In
Figure 1: Block diagram <strong>of</strong> the LFEX-Laser.
addition, the “Gekko-EXA” Laser with a higher peak
power has been under a conceptual design to improve the
fusion researches and to open the new high field
researches in the plasma physics.
LFEX-LASER
The LFEX laser generates 10 kJ pico-seconds pulse
energy with four beams by using a chirped-pulse
amplification (CPA) technique, which corresponds
to several peta-watts peak power. The laser system
consists <strong>of</strong> a front end, rod amplifier chains, a main
amplifier, and rear end (pulse compression), shown in fig.
1. A front end is a combination <strong>of</strong> a mode-locked fibre
oscillator, two pulse stretchers and three optical
parametric chirped-pulse amplification (OPCPA) stages.
The OPCPA stages are used instead <strong>of</strong> a conventional
regenerative amplifier to improve the temporal pulse
contrast. Much care <strong>of</strong> a beam transport with image relays
are taken not to make the beam quality inferior. The
maximum pulse energy is obtained up to 100 mJ in fig. 2.
The typical pulse duration is 3 ns with a 6 nm spectral
width at a 1053 nm centre wavelength. After four-pass
Nd:glass rod (φ50mm)-amplification (RA), the amplified
beam is divided into four beams and each beam
experiences two rod-amplifiers to obtain about 10 J pulse
energy. The main amplifier is a four-pass amplifier with a
Nd:glass slab amplifier and a long image relay. Eight
large slab glasses (46 cm x 81 cm x t4cm) are used for