Spatial color-encoded phase-shifting technique for phase measuring deflectometry

Free-form optics has been attracted huge interest since it can significantly improve the performance of an optical system with a simpler structure. However, optical testing for free-form surfaces is usually more difficult compared with traditional ones. Although a variety of interferometers can achieve measurements with nanometer-scale precision, it suffers from the problems of a complex system configuration, a limited measurement range and relatively high requirements of testing conditions, etc. In contrast, phase measuring deflectometry (PMD) which has the benefits of a simple system structure, a large dynamic range and a high measurement accuracy is gradually becoming a powerful tool for free-form surface testing. Nevertheless, multiple groups of fringe patterns are required to sequentially display in two orthogonal directions to obtain the corresponding surface gradients in the classical PMD measurement. Therefore, a speedy detection of free-form surfaces is generally blocked. To overcome the above shortcoming, a spatial color-encoded phase-shifting strategy is put forward for PMD to acquire absolute phases with only four color images in this paper. Experimental results demonstrate the effectiveness of the proposed method as well.