对大口径离轴非球面进行零位补偿检测时, 投影畸变过于严重的区域会由于干涉条纹密度过大而无法检测, 从而使加工难以进行。针对此问题, 本文采用相对畸变参数定量描述投影畸变, 设计了自由度更高、补偿能力更强的计算全息图(CGH)检测方法。该方法在CGH设计阶段考虑投影畸变分布, 选择合适的光路结构使得所有区域的投影畸变均较小。根据此方法, 对直径为1.45 m的离轴非球面设计了比零位补偿器畸变小的CGH。 检测实验显示: 使用设计的CGH可检测非球面的全口径面形误差, 验证了在CGH设计阶段考虑投影畸变的正确性与实用性, 表明该方法可解决加工过程中零位补偿器由于投影畸变导致部分区域不能检测的问题。以CGH的检测结果为指导, 目前该1.45 m直径的离轴非球面加工精度已达0.374λ PV, 0.023λ RMS。

In the process of an asphere fabricating, the part with large mapping distortion in the large caliber off-axis asphere may not be measured by an interferometer due to larger interferometric fringe density. To solve this problem, the parameter named related distortion was used to describe the mapping distortion quantitatively, and a Computer Generated Hologram(CGH) with higher freedom and stronger compensation ability was designed. By taking the mapping distortion distribution into account, the method selected a proper path and allowed all the aspheric surface to have smaller mapping distortion in the design of the CGH. With the method, a CGH with proper paths was designed for testing the 1.45 m off-axis asphere, by which the full map distortion of the system is less than that of the traditional null-lens compensator. The test experiment shows that the designed CGH can test the full map error of the off-axis asphere, which verifies the validity and practicability of the proposed CGH design method and demonstrates that designed CGH with considering test mapping distortion has solved the problem as mentioned above. By this method, the map errors of 1.45 m diameter off-axis asphere are 0.374λ PV and 0.023λ RMS now.