Two-dimensional coupled wave theory is used to calculate spatial dispersion of the diffraction pulse through volume
Bragg grating (VBG). Results indicate that the spatial dispersion, which describes the spatial chirp and reflects globally
how far different frequency components separate, is influenced by the grating parameters, wavelength and the
propagation distance. To two ultrashort pulses with different durations (100fs, 20fs), the degree of spatial broadening
through the VBG and the propagation process is both presented. The approach provides a theoretical foundation to
design proper volume Bragg gratings for redressing the spatial chirp in the ultrashort-pulse laser system.