Preliminary design of technical integration line (TIL) for SG-III laser facility

In this paper, we present the preliminary design of Technical Integration Line (TIL). TIL is a full scale 4 x 2 module of Shenguang-III(SG-III) laser facility with a two-aperture(25 x 25cm(2)) output of 3.0kJ at 3 omega in a temporally shaped pulse of 1.0 similar to 3.0ns. The goal of TIL is to demonstrate the laser technology of the proposed SG-III. TIL is consisted of front-end, preamplifier stage, main amplifier stage, diagnostic target system and control system and the average fluency is designed to operate at 5.0J/cm(2) in a 1.0 ns output purse. The optical scheme of a four-pass main amplifier(A1) and a booster amplifier(A2) have been chosen. The clear aperture of amplifier is 30 x 30cm(2), and the numbers of Nd:glass disks in the two amplifiers are optimized in system design. Two spatial filters are inserted in the system to remove high spatial frequencies from the beam, and SF1 is the multi-pass spatial filter and SF2 is the transport spatial filter. In order to correct the output wavefront for static and dynamic wavefront aberrations of disk amplifiers, a deformable mirror system is used in the main amplifier stage of TIL. It is different from the French Laser Megajoule (LMJ) that the small aperture laser beam from preamplifier is injected into the cavity through SF1, and is amplified by Al for the first two passes. The beam reverser in SF1 uses small mirrors and lenses to redirect the beam for another two passes. The beam aperture is 20 x 20cm(2) in A1 and then expands to 25 x 25cm(2) by SF1 to increase the filling factor of A2. A large aperture plasma electrode Pockels Cell PC2 is inserted between the cavity mirror and A1 to isolate backward beam or pencil beam in the system after the main pulse and a small Pockels Cell is used in beam reverser to suppress parasitic oscillations in the cavity before the main pulse. Thus, both Pockels Cells operate in static state to reduce difficulties in developing large aperture Pockels Cell and cost. There is only one large reflecting mirror in the cavity of A1 and the alignment accuracy and stability of the system can be increased.