离轴非球面的计算全息图高精度检测技术

Test of off-axis aspheric surfaces with CGH

为了实现离轴非球面高精度定位、光路对准及面形检验,提出了一种使用计算全息图(CGH)技术实现离轴非球面高精度光学检测的方法。将被检非球面倾斜平移后作为轴上自由曲面进行CGH补偿检测设计,从而减小了检测光路的相对口径和CGH所需补偿像差,提高了CGH检测精度。使用自行开发的CGH专用设计计算软件,设计完成的CGH同时具有非球面检验、检测光路对准、被检非球面基准定位等多项功能。采用该方法设计(设计精度优于λ/10 000rms)并制作CGH对面形精度优于λ/50rms的离轴非球面进行了检测,误差分析表明,其检测精度优于λ/100,与传统null-lens方法的检测结果精确吻合。实验表明,采用该CGH可同时实现离轴非球面位置高精度定位、CGH与干涉仪对准以及离轴非球面高精度面形检验。

A new test method based on a Computer-generate Hologram（CGH） was presented for precisely testing off-axis aspheric surfaces and aligning the optics in tests.In this method,off-axis aspheric surfaces were tilt-translated and tested as an on-axis freeform optics to minimize the wavefront compensation and to reduce the relative aperture of the test setup.A software was developed to design the CGH to implement three kinds of diffractive sections,i.e.compensating wavefront in null test,alignmenting the optical path by adjusting the relative position between CGH and interferometer,and projecting fiducial marks around the optics.As an example,a typical off-axis aspheric surface with a figure error less than λ/50 rms was tested in this method.Results indicate that the CGH design error is better than λ/10 000 rms and the total error is better than λ/100 rms.These data agree well with the test result with null lens.The experiment also verifies the feasibility of alignment and fiducial sections and demonstrates that cross-lines projected by CGHs can be used as fiduciary to guide the alignment of the optics and measure the off-axis distance.