The Integration Test Bed (ITB) is a large-aperture single-beam Nd:glass laser system, built to demonstrate the key technology and performance of the laser drivers. The phase II designed output of the ITB at 1053nm is 18.2kJ with the peak power of 3.6TW. So it is important to keep a flat spatial intensity profile at the end of the system to avoid optical elements damage or small-scale self-focusing. Applying the Liquid Crystal Programmable Spatial Shaper (LCPSS) to compensate the beam non-uniformity related to amplification and transmission is an effective way at present. In this paper, we attempt to pre-compensate the beam nonuniformity by the LCPSS. Experiments were carried out to study the spatial fluence modulation and contrast improvement at the main laser output of the ITB laser facility. The results show that the peak-to-average fluence modulation in the near-field is typically 1.35:1; the contrast is about 0.08, at the designed energy and power, which meet the modulation less than 1.4:1 and the contrast under 0.1 design requirement.
Based on the multiple pulses joining, the cascaded photodetection is experimentally researched on high-contrast measurement of ns high-power laser pulse. The ultrafast photodetectors with the saturation characteristics are used. A joining method for multi-pulse waveforms in the nonlinear region is put forward. The experimental results for ns step-pulse at SG-III laser system show the contrast of ~ 400:1 is achieved, in accord with designed contrast value.
The Integration Test Bed (ITB) is a large-aperture single-beam Nd:glass laser system, built to demonstrate the
key technology and performance of the laser drivers. It uses two multipass slab amplifiers. There are four
passes through the main amplifier and three passes through the booster amplifier. The output beam size is
360mm by 360mm, at the level of 1% of the top fluence. The designed output energy of ITB at 1053nm is
15kJ in a 5ns flat-in-time (FIT) pulse, the third harmonic conversion efficiency is higher than 70%. The first
phase of the ITB has been completed in July 2013. A series of experiments demonstrated that laser
performance meets or exceeds original design requirements. It has achieved maximum energies at 1053nm of
19.6kJ at 5ns and 21.5kJ at 10ns. Based on a pair of split third harmonic generation KDP crystals, the third
harmonic conversion efficiency of about 70% and 3ω mean fluences as high as 8.4 J/cm<sup>2</sup> have been obtained
with 5ns FIT pulse.