Comprehensive measurement system for surface topography and focal length of microlens arrays based on a Twyman-Green interometer and the axial-scanning-assisted angular method

Abstract

Surface topography and focal length are two key parameters of microlens arrays that directly determine their optical performance. Conventional characterization methods generally require two independent measurement systems for topography and focal length, making it difficult to establish precise spatial correspondence between the results. In this paper, a comprehensive measurement system is proposed by integrating a Twyman-Green interferometric optical path with a focal length measurement path based on the proposed Axial-scanning-assisted Angular Method. The system enables measurement of surface topography and focal length within the same region of the sample without repositioning the specimen or reconfiguring the optical setup, thereby achieving micrometer-level matching between the two sets of results. To evaluate the system performance, experiments were conducted on a microlens array sample with a microlens element diameter of 100 μm and a radius of curvature of 507 μm. The results indicate that the surface topography measurement accuracy reaches 13 nm RMS and 109 nm PV, while the focal length measurement accuracy is 2.72 %. Furthermore, the average inter-subsystem alignment deviation, verified across five microlens elements, is 8.04 μm, with a standard deviation of 2.19 μm.