Measuring Axicon Surface By Using Annular Sub-Aperture Scanning Method

Herein, a novel method for measuring axicon surface based on annular sub -aperture scanning is proposed. This method successfully performs the general measurement of axicon surfaces with a large diameter and different cone angles. A micro-motion scanner is used to move the axicon step by step while the wave measuring interferometer records several ring phases in the normal direction of axicon. The surface is computed by extracting effective pixels and the interpolation -stitching. The proposed method successfully measures an axicon with a cone angle greater than 96.1 and a diameter above 100 mm. Results in the normal direction of the surface arc exclusively used, and a theoretical measurement accuracy up to lambda/4 PV (lambda is wavelength; PV is peak valley) is achieved. In the experiments, the top surface of a convex axicon (with a nominal angle of 140 degrees) is measured by a 4-inch (1 inch= 2. 54 cm) DynaFiz interferometer of ZYGO company. Two measurements arc performed with the axicon rotated at 90 degrees. Both results arc in good agreement with the measurement results of the LuphoScan profiler of Taylor-Hobson company, and the difference in PV values is 0. 51 mu m. These results demonstrate the good feasibility of the proposed method.