On November 15-16, 2021, more than 70MeV proton beam was achieved on PetaWatt laser of Shenguang II (SG II) 9^th Beam, in Shanghai Institute of Optics and Mechanics. This is the highest output proton based on the Target Back Sheath Field Acceleration Mechanism (TNSA) in laser-driven proton acceleration experiments, which is carried out by researchers form Shanghai Laser Plasma Research Institute.
Laser signal-to-noise ratio and focal spot parameters in SG II 9^th beam have been significantly improved by applying new technologies, such as OPCPA (first online application of PS-OPA), CPA energy flow and isolation optimization, transmittance enhancement and focal spot optimization, from April to November in 2021, which played a key role in improving the results of physical experiments.

Fig 1 (a) Contrast of OPCPA output, (b) SN of ns laser (Image by SIOM)

Fig 2 (a) Focal spot of output, (b) Recordings of RCF (Image by SIOM)