Test of vertex radius and conic constant of a conic surface by means of interferometry

The vertex radius of conic (vertex ROC) and conic constant (CC) are important shape parameters for conic surface. An interferometric method that can determine these two parameters by comparing the sub-surface with a spherical reference wavefront equal to local sagittal, medial or tangential ROC is introduced in detail. The measured wavefront aberrations, particularly astigmatism and coma, and local radius difference are used to calculate vertex ROC and CC. The influence factors on measurement accuracy are analyzed and an effective method for reducing such influences is also presented. According to the mathematic model, the programs to simulate the test results numerically are compiled by Matlab. © 2009 SPIE.