diffraction integration. In the single Fourier transform method，the sampling of quadratic phase factor and the size of

the calculation window can seriously affect the calculation accuracy. Based on the concept of local spatial frequency

and the sampling theorem，this paper gives the ideal sampling interval of quadratic phase factor and the selection

method of the size of the calculation window. Then the numerical simulation results are compared with the

theoretical analytical solutions and experimental results，respectively，to verify the effectiveness of the ideal

sampling interval and the selection method of the size of the calculation window.