Abstract: Based on the method of wavefront analyses and the Kirchhoff diffraction integral expression, we derive the complex amplitude distribution along axis of Fresnel diffraction fields by a circular aperture or a half-circular aperture, which is illuminated by a convergence spherical wave. The phase distribution is especially focused and the phase difference formula between both symmetrical points beside the image point is given. The result shows that the phase change pass through the image point is continuous. Then the present result is applied to the bihalf-lens i. e. , the Meslin interference experiment. The phase difference formula as well as the intensity distribution between two diffraction fields respectively by a single half-lens are shown under two different situations, one is the focal lengths equal while the object distances not equal, another is the object distances equal while the focal lengths not equal. The results lead to a conclusion： the effective phase difference along axis between both two diffraction fields may be not equal to zero or π, it is also possibility to arise a change of this phase difference as a sawtooth form. This study provides a reliable theoretical way to exactly analyze the interference field from two diffraction fields by bihalf-lens.

Key words: Fresnel diffraction, Fresnel-Kirchhoff diffraction integral expression, wavefront phase-factor analyses, bihalf-lens interference