Compared with amplitude splitting method, wavefront splitting method is another method to realize interference. The wavefront of point light source is divided into two parts, which pass through two optical groups respectively, and overlap after reflection, refraction or diffraction, forming interference in a certain area.

Since any part of the wavefront can be regarded as a new light source and all parts of the same wavefront have the same phase, these separated parts of the wavefront can be regarded as light sources with the same initial phase, and the initial phase difference of these light sources is constant no matter how fast the phase of the point light source changes. Young's double slit, Fresnel double mirror and Loew mirror are all such wavefront interferometer devices.

Limitation of fractional wavefront and its application;

Whether interference fringes appear in wavefront splitting method is limited by the spatial coherence of light source. Point light source has the best spatial coherence, which is coherent in the whole space. Therefore, when the wavefront is divided, the interference fringes can be obtained by taking the wavefront in any far area. The spatial coherence of extended light source is not high. When dividing the wavefront, interference fringes can only be obtained by limiting different regions to a range with good spatial coherence.

Judging the light source:

The best example of judging the size of light source by spatial coherence is Michelson star interferometer. 180 1 year, Thomas Young, an Englishman, realized light interference with ordinary light sources. The experiment is ingenious in conception, simple in device and obvious in fringe, which is of great significance in wave optics. It has become one of the theoretical foundations of the wave theory of light and is considered as one of the most beautiful experiments in physics.