Measurement of large off-axis convex asphere by systemic stitching testing method

In order to overcome the difficulty of testing large off-axis convex asphere, the convex asphere systemic stitching testing method combining with wave aberration testing and subaperture stitching interferometry(SSI) is proposed.The basic principle and flow chart of this method are analyzed and researched, and the stitching mathematical model is established.When the primary mirror and second mirror of the three mirror astigmatism(TMA) system have been fabricated, we align and calibrate the optical system, and test wave aberration of all the fields successively.Then we can obtain the phase map of the whole aperture by the synthetical optimization stitching algorithm and interpolation, which provides the guarantee of the subsequent fabrication and systemic testing.With engineering examples, a large convex mirror with the aperture of 287 mm×115 mm is tested by the method, and the value of RMS of the surface error is close to 1/30 λ( λ=632.8 nm) after two cycles of fabricating and testing.