介绍了一种由光束在焦面附近几个面上的强度分布重构出光束近场波前的方法。把波前重构问题作为一个非线性优化问题, 利用光束口径区域内的正交多项式模拟光束波前相位分布, 通过优化多项式各项的系数, 使对应的波前分布在焦面附近相应的几个面上的强度分布与已知强度分布的偏差最小, 即认为由此时的多项式系数决定的近场波前代表了真实的光束波前。针对方光束口径, 利用Legendre多项式模拟光束波前分布, 利用共轭梯度算法对多项式系数进行了优化计算；优化过程分为几步进行以减少计算时间。重构得到的波前分布与参考波前分布符合得很好。

A simple method is introduced to reconstruct the nearfield wave-front from intensity distribution near foal plane, which is treated in this paper as an optimization problem. Proper orthogonal decomposition technique is applied to describe the wave-front to be reconstructed. By optimizing the coefficients of the polynomial to minimize the differences between simulated intensity distributions and the real intensity distributions, nearfield wave-front can be reconstructed and characterized. Simulations are carried out upon square-aperture beam using Legendre polynomial. Conjugate gradient method is used and optimization is performed for several steps to reduce executing time. The results show that the reconstructed wave-front are consistent well with the reference wave-front.