Improvement of focusing performance for a multi-petawatt OPCPA laser facility

In the paper, we demonstrate improvement of the focused intensity for a multi-petawatt optical parametric chirped-pulse amplification laser facility by several methods. An adaptive optics system with a large-size deformable mirror is employed and it applies a closed-loop correction method based on detection of the on-target focal spot rather than wavefront. In addition, a pair of achromatic lenses is designed and utilized to compensate chromatic and spherical aberrations of the laser system. Moreover, the additional dynamic aberrations introduced by 3-stage optical parametric amplifiers are investigated experimentally. After optimization, the focal spot size (full width at half maximum, FWHM) is 3.3 mu m x 4.0 mu m in x-axis and y-axis directions and the enclosed energy in FWHM is 28% when an on-axis parabolic mirror with a focal length of 800mm is used. The focused intensity of similar to 4 x 10(21) W cm(-2) has been achieved for a 1.6 PW shot. The laser intensity is expected to be 10(22) W cm(-2) or higher for 4.9 PW peak power.