Fig. 1. Schematic diagram of single-beam optical path and base frequency near-field monitoring point distribution (monitoring point 1) of SG-II UP grade facility

Fig. 2. Schematic diagram two-dimensional distribution of base frequency near-field of SG-II UP grade facility. (a) No.20220909008;

Fig. 3. Diagram of near-field beam fluctuation

Fig. 4. Characteristics of successive signals and the fitting curve of signal fluence and average energy density. (a) Signal fluence;

Fig. 5. Probability density curves simulation. (a) Probability density curves of relative fluence distributions at different contrasts;

Fig. 6. Relative fluence distributions, Gaussian fits and 2D distributions for different near-field beams. (a) 7th laser No.20220906006; (b) 1st laser No.20220906012; (c) 5th laser No.20220906012; (d) 5th laser No.20220914005

Fig. 7. Schematic diagram of fundamental frequency near-field image segmentation results. (a) Original near-field image; (b) near-field image processed by automatic correction algorithm; (c) near-field image with 85% area; (d) schematic diagram of near-field image region division (5×5) results

Fig. 8. Local contrast change curve of the 7th laser beam (No.20220906006) of SG-II UP grade facility

Fig. 9. Calculation results of different beams contrast, modulation, and local modulation for specific shots. (a) Calculation results of contrast and modulation; (b) local modulation for the 10th, 15th, 30th, and 48th shots, with horizontal coordinates corresponding to 25 areas shown in Fig. 7(d)

Fig. 10. Schematic diagram of 2D fluence distribution in the 24th region of laser beam. (a) 10th shot; (b) 15th shot; (c) 30th shot; (d) 48th shot

Fig. 11. Local modulation for 3 shots of 1st laser of SG-II upgrade facility between March and April 2020, with horizontal coordinates corresponding to 25 areas shown in Fig. 7 (d)

Fig. 12. Near-field output images of 3 shots of the 1st laser of SG-II UP grade facility in 2020

Fig. 13. Variation curve of the 5th region of modulation of the 1st laser of SG-II UP grade facility between March and April 2020

Fig. 14. Schematic diagram of evolution of near-field high fluence region at fundamental frequency near-filed of the 1st laser in 2020

Fig. 15. Distribution characteristics diagram of the number of high-fluence pixel versus signal to noise ratio

Fig. 16. Variation curve of the number of high-fluence pixel versus signal to noise ratio