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A dual-fiber point diffraction interferometer is built to measure the wavefront aberration of an imaging system with high precision. The optical intensity of the test light and reference light are controlled independently, so that high interference contrast can be obtained. The interferometer has several advantages: high precision, a flexible structure, and a quasi-common optical path. System errors of the interferometer that influence the measurement accuracy are considered and calibrated. In the experiments, a projection lens with numerical aperture of 0.3 is measured. The measured wavefront error is 1.5 nm rms, and the measurement repeatability is 35 pm rms.

We propose a noncontact method for measuring the cone angle of an axicon. A microscanning stage moves the axicon being tested while a Fizeau interferometer is recording the scanning interferograms. The cone angle is measured accurately with the axial moving distance and the phase change calculated from interference fringe counting. Numerical analysis discusses the influence of standard deviation of the interference fringe count and the standard deviation of the scanning distance. Three methods for systematic error calibration are also proposed. This approach can measure both concave and convex axicons with a cone angle in the range of 96.4 deg to 170 deg. The measurable diameter of the axicon exceeds 100 mm. The spatial distribution of cone angle can be obtained with a resolution from 300 μm to 1 mm. The theoretical measurement accuracy is better than 10″ when the scanning distance is 1000 μm, and the positioning error is

Nonflatness of stage mirror surface affects the position accuracy of the wafer stage in lithography tool. Precise surface flatness measurement is needed for the computer controlled polishing of stage mirror. A subaperture stitching system using a commercial 4-inch Fizeau interferometer was presented in this paper. Absolute test was used to calibrate the surface figure of the reference mirror with the accuracy better than λ/100 PV (λ = 632.8nm）. Subaperture stitching was used to extend the measurement aperture larger than 450×50mm. Stitching measurements were carried out for stage mirrors during surface polishing. Comparison tests were also made with a 24-inch interferometer. The results show that the stitching system has the advantages of larger dynamic range, higher spatial resolution, and better measurement accuracy in local area.