Subaperture stitching interferometry for testing a large hyperboloid

In order to test large aspheric surfaces without the aid of null optics, a novel method called subaperture stitching interferometry (SSI) is presented. The synthetical optimization stitching model are established based on homogeneous coordinate's transform and simultaneous least-squares fitting. A prototype of testing large aspheres is developed by the stitching method. The experiment of testing a hyperboloid with SSI is carried out. The PV and RMS of the surface are 0.319λ and 0.044λ (is 632.8 nm) respectively when five subapertures are stitched together. For comparison and validation, the asphere is also measured by null testing. It is shown that the two testing results consist with each other, PV and RMS error are 0.032λ and 0.004λ respectively. Thus, it can be concluded that the algorithm and model of the SSI technology are feasible for the testing of large aspheric surfaces, which provides the probability of testing the mirror with large aperture and asphericity in non-null configuration.