Surface measurement with Shack-Hartmann wavefront sensing technology

Abstract

When wavefront is reflected by a surface, the information of the surface profile is carried by the reflected wavefront. Measure the wavefront can extract the profile information. There are different kinds of pre-defined surface profile with various dimensions. While the size of particular wavefront sensor is fixed, the measurement range is limited. The design of optical system to bridge the work piece and wavefront sensor is critical. This paper presents a platform for the guidance of optical system design. The parameters of commercial available optical components are input to the platforms and the propagation of reflected wavefront is simulated. The relationship of part profile and the measurement wavefront is provided. The discussion is focused on the 2f+2f system for surface flatness measurement. The measurement of aspherical surface is also presented. Shack-Hartmann wavefront sensor (SHWS) is selected due to its simple structure, insensitivity to vibration etc, which is suitable for in-line application. Optical system is designed with the guidance of simulation platform. The experimental results shows the 2f+2f system is compatible to misalignments, can be used to monitor the deformations of parts. The measurement of aspherical surface is also presented with the comparison of simulation results.