Based on diffraction integral formula and selfreproducing principle,diffraction integral equation for transverse modes in a circular symmetric resonator with an aperture diaphragm was disintegrated to finitesum matrix equation,and field distributions of transverse modes in the resonator were calculated by solving matrix for eigenvalues and eigenvectors.

According to the basic relation E =φ/A, a direct optical method for aperture area measurement was provided, based on known constant irradiance over the aperture.

The Stabilization Analysis of Automatically Adjustable Optical intensity System Using Iris Diaphragm;

In this method,light was adjusted by combining external trigger electronic shutter mainly and iris diaphragm assistantly.

Because of the illuminance of external world change with train working, we can change the iris diaphragm size and adjust shutter exposure time access to the best of the CCD exposure, So as to achieve good results observed.