Non-Null Interferometers For Irregular Surface Measurement With System Modeling

A design method of non-null interferometers is proposed in this paper for measuring irregular surfaces such as optical aspherics, freeform surfaces and droplet surfaces. With system modeling and raytracing, the improved reverse optimization reconstruction method is employed to correct the retrace error and obtain the accurate shape of the test part with all frequency information. To simplify the model in the raytracing program, an imaging lens images the desired interferogram at a certain plane on the detector and, therefore, only the test arm needs to be modeled. The imaging error of an interferogram, which can be reduced by the partial compensation system (PCS), is analyzed, and the design of the PCS is also demonstrated. Two cases with different optical layouts show the feasibility and the versatility of our method.