“…Several studies have discussed how to generate the doughnut beam [10][11][12]. In a previous study by Xie et al, a numerical study was done in the case studies where there was not lateral offset [13], and it was suggested that the impulse could be higher with a doughnut beam than with a singlespot beam [14,15], owing to the shock focusing effect [16][17][18][19]. However, such a shock focusing effect on the impulse enhancement has not been verified experimentally.…”