Abstract: In order to evaluate absolute accuracy of point diffraction interferometer(PDI), a system error calibration method based on tilting and rotation of test mirror is used and calibration algorithm are discussed in detail. Calibration formulas are deduced and a verified simulation is conducted. In the method, figure errors of spherical test mirror are measured in N equal position around an initial axis and a tilt axis. The rotationally asymmetric component of real figure about test mirror in each axis position can be calculated through rotation method. As system errors in same coordinate are constant in two rotate measurements, subtract one from another, an equation can be acquired without system error term. The rotationally symmetric component of real figure which expressed in Zernike rotationally items can be evaluated in solving this differential equation with least square. System error can be acquired through deprive real figure error of test mirror from measurement data. The simulation results shows that figure error of test mirror and system error which calculated through this algorithm are consistent with the simulation input values, difference of errors are less than 0.03 nm and residual errors are less than 0.3 nm, it can meet the requirement of the calibration accuracy.

Key words: Diffraction wavefront, Figure error, Point diffraction, Rotationally asymmetric, Rotationally symmetric