Measuring cone angle of axicon using scanning Fizeau interferometer.

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 <10 nm. Experiments have been carried out to prove the feasibility of the proposed method, a 140-deg convex axicon is measured, and the measurement repeatability is ~6". [ABSTRACT FROM AUTHOR]