Square Region On The Wave Mode Description Of The Icf System

Laser was used as driver of the Initial Confinement Fusion (ICF) system. One of the key parameters is the quality of laser wavefront. Usually the Peak-to-Valley value (PV), Root-Mean-Square of gradient (GRMS) and Power Spectral Density (PSD) were used to describe the wavefront. But they didn't give us much information about the spatial characteristic of the wavefront. It's important to establish a set of orthonormal aberration modes for expanding the laser wavefront.Currently most of the studies were concentrated on the wavefront expanding methods for the circular and annual aperture system. There is still no orthonormal base function for expanding the wavefront on square aperture. In this article the modal expanding problem for the square aperture was investigated.First the application of circle Zernike polynomials on the square aperture system was studied. It shows that it's possible to expand the square wavefront with circle Zernike polynomials if enough prior knowledge is given. But the mode coefficients cannot be used directly to calculate the parameters of certain aberration mode.A new set of orthonormal base functions for use on square aperture was constructed based on the circle Zernike polynomials. Besides the orthonormal property, there is a simple relationship between the coefficients of square Zernike polynomials and the classic Seidel aberration coefficients. Also there is a simple relationship between the coefficients and the wavefront variance. A study about how to detect the square Zernike modes using Hartmann-Shack wavefront sensor was conducted and the method of how to select the lens array size was given.The application of square Zernike polynomials in the Shenguang-III prototype facility was studied. And the results of the wavefront aberration spatial characteristic were used in the design process of optical system architecture of Shenguang-III prototype. Also the dynamic wavefront of laser shot and the thermal recovery process was studied.