Abstract: Based on the scalar diffraction theory and the boundary condition of Rayleigh-Sommerfeld, the accurate on-axis propagating wave function of plane wave diffracted by small circular band is obtained by solving the first integral of Rayleigh-Sommerfeld. By means of the function, the extremas of on-axis light intensity, the locations and number as a function of the radius of small circular band are analyzed,and then extend the conclusion as the inner radius trends to zero or outer radius trends to infinity. This study offers the conclusion not only for the application of engineering and technology but also for the optics education.

Key words: diffraction of circular band, plane wave, the first integral of Rayleigh-Sommerfeld, Fresnel number