Analysis of the errors between measurement and simulation of near field for highintensity

1w and 3 w near field beam quality for highintensity THG have been measured, and 3 w near field beam quality measured in experiments is compared with that simulated and calculated. Especially, the errors produced in simulation and calculation of near field beam quality for highintensity THG are investigated. By analyzing major factors not being considered that affect 3w near field beam quality in simulation and calculation, it is suggested that the simulating code be improved. Indispensable methods are discussed to improve 3w near field beam quality. The article is of reference value for further study on theories and experiments．