PERFORMANCE OF A PROTOTYPE FOR A LARGE-APERTURE MULTIPASS ND-GLASS LASER FOR INERTIAL CONFINEMENT FUSION

The Beamlet is a single-beam prototype of future multibeam megajoule-c lass Nd:glass laser drivers for inertial confinement fusion. It uses a multipass main amplifier, adaptive optics, and efficient, high-fluenc e frequency conversion to the third harmonic. The Beamlet amplifier co ntains Brewster-angle glass slabs with a clear aperture of 39 cm x 39 cm and a full-aperture plasma-electrode Pockels cell switch. It has be en successfully tested over a range of pulse lengths from 1-10 ns up t o energies at 1.053 mu m of 5.8 kJ at 1 ns and 17.3 kJ at 10 ns. A 39- actuator deformable mirror corrects the beam quality to a Strehl ratio of as much as 0.4. The 1.053-mu m output has been converted to the th ird harmonic at efficiencies as high as 80% and fluences as high as 8. 7 J/cm(2) for 3-ns pulses. (C) 1997 Optical Society of America.