Fresnel diffraction of a plane transmission grating

Based on Fresnel diffraction theory,the diffraction field of a spherical wave through a plane trans- mission grating is studied in detail.The amplitude distribution of Fresnel diffraction and a calculation formula for Fresnel diffraction angle of a grating are given.The waves in each order of Fresnel diffraction are spherical wav- es under ideal conditions.The diffraction angles can still be given by the grating equation of Fraunhofer diffrac- tion after Fresnel diffraction angle is redefined.