title: Adaptive centroid-finding algorithm for freeform surface measurements.
abstract: Wavefront sensing systems measure the slope or curvature of a surface by calculating the centroid displacement of two focal spot images. Accurately finding the centroid of each focal spot determines the measurement results. This paper studied several widely used centroid-finding techniques and observed that thresholding is the most critical factor affecting the centroid-finding accuracy. Since the focal spot image of a freeform surface usually suffers from various types of image degradation, it is difficult and sometimes impossible to set a best threshold value for the whole image. We propose an adaptive centroid-finding algorithm to tackle this problem and have experimentally proven its effectiveness in measuring freeform surfaces.
authors.affiliation: Optical Metrology Group, National Metrology Center, Singapore. wjguo.student@simtech.a-star.edu.sg
authors.forename: Wenjiang
authors.initials: W
authors.lastname: Guo
authors.forename: Liping
authors.initials: L
authors.lastname: Zhao
authors.forename: Chin Shi
authors.initials: CS
authors.lastname: Tong
authors.forename: Chen
authors.initials: C
authors.lastname: I-Ming
authors.forename: Sunil Chandrakant
authors.initials: SC
authors.lastname: Joshi