It is showed that a shock wave speed distribution in red light period at a plane intersection satisfies a normal assumption, as well as Poisson assumption.
Starting from the wave differential equation, a method is deduced to express the complex amplitude of lightwave fields in the reference plane which is vertical to the optical axis.
Based on the accurate expression of light intensity at transverse plane, the propagation characteristics of monochromatic planar wave diffracted by small circular aperture are analyzed in this paper.