光学自由曲面元件如离轴非球面等在现代光学系统中起到了越来越重要的作用。计算全息元件(CGH)可产生任意形状的波前，能够很好地应用在光学自由曲面的零位补偿干涉测量中。针对一离轴椭球面为测量样品，以光学计量领域比较成熟的Offner补偿器法，测量离轴非球面母镜的面形偏差，进而获得离轴椭球面的面形偏差；再将离轴椭球面通过旋转平移，作为自由曲面元件，在平面基板上设计CGH对其进行零位补偿测量，研究零位补偿CGH的误差传递数据。通过主要原理误差分析与计算，在光学熔石英平面基底上制作零位补偿CGH，测量不确定度达到λ/10[峰谷(PV)值, λ=0 .6328 μm]，满足光学自由曲面元件的高精度检测要求。

Optical freeform surface acts an important role in modern optical system. Computer generated hologram which can generate arbitrary wavefronts shows great advantages in the null test of optical freeform surfaces. According to an off-axis aspheric surface, the surface shape deviation can be gotten by testing the initial aspheric surface with Offner compensator. The off-axis aspheric surface lacks of symmetry can be regarded as freeform surface by rotation and translation in the optical path, and a CGH null compensator is designed on flat substrate to achieve null test of the freeform surface. With calculation and analysis of the main errors in the CGH null test, the measurement uncertainty of freeform surface test can reach λ/10[peak- valley(PV) value] level. CGH compensator can be used in the high precision test of freeform surface.