为了实现极紫外光刻(EUVL)投影物镜光学元件均方根(RMS)0.2~0.3 nm的面形检测精度要求，研究了超高精度光学元件检测方法。采用误差分解控制方法，设计了非球面补偿器检测系统。补偿器由提供透射球面波的前组元件及产生非球面分量的球面元件组成，可通过对补偿器前组的标定及后组元件的参数控制保证系统测量精度。分析了非球面补偿器检测系统的主要误差来源，提出了环境误差及补偿器前组波像差的控制参数，通过误差分类评估了系统检测精度。非球面补偿器的检测RMS达0.245 nm，能够实现超高精度的极紫外光刻非球面元件检测。

Calling for diffraction limited imaging performance, extreme ultraviolet lithography (EUVL) demands unprecedented requirements for figure metrology. The asphererical surface of EUVL mirrors must be measured with higher accuracy. Root mean square (RMS) is 0.2~0.3 nm. The design of interferometric null metrology is focused on, which can produce such highly precise figure of aspherical surfaces. The null lens is splited into a transmission sphere and a single lens. The errors introduced by the interferometer and the transmission sphere can be calibrated, and the error from the single lens can be rigidly controlled to guarantee the system testing accuracy. The residual aberration of the null testing system is controlled to be smaller than 0.003λ in the system. The main error sources of the null testing system are analyzed, the parameters of environmental control are proposed as well as limite residual aberration of the transmission sphere. Furthermore, the error sources are classified and the measurement accuracy of our aspherical null testing system is evaluated, RMS reaches 0.245 nm. It can meet the requirements of EUVL optics testing.