Research On Long Curvature Radius Measurement Method Based On Planar Interferometer

Radius of curvature (ROC) is one of the fundamental optical structural parameters of spherical optics. With the development of large-scale optical systems, such as large telescope systems and giant lasers, the spherical optics with long ROC as well as high accuracy are in great need. Optical interferometry is one of the effective methods for non-contact measurement of large ROC with high accuracy and sensitivity.In order to measure the radius of curvature of the spherical surface with high accuracy, which the radius of curvature is about 40 meters, a novel Newton’s rings method is proposed with the plane interferometer for measuring the laser cavity, which is a spherical mirror with the nominal ROC of 41400 mm and the test value of 41350 mm by using Taylor Hobson profilometer. For the classical Newton’s rings are dense and the variation Newton ring’s method needs a real spherical template, the moire variation Newton’s ring’s method was proposed. In the Moire variation Newton’s rings method, the virtual Newton’s rings were superposed with the actual Newton’s rings. In order to effectively extract the dark ring position of Newton’s rings, the second-order polar coordinate transformation was used, which transformed the circular fringes into line fringes. By the moire variation Newton’s rings method, the one-dimensional radius of curvature was acquired, which is 0.5% contrast with profilometer measurement results. For using the two-dimensional information of interferogram effectively, the phase-shifting interference method wave-front reconstruction algorithm was applied for obtaining the differential wave-front of virtual and actual. According to the special model, the two-dimensional radius of curvature was acquired, which is 1.1% contrast with profilometer measurement results. The retrace error was existent in the reflected wave of reference wave, so the retrace error in the measurement system was calibrated by the multi-configuration model in ZEMAX. After compensating the retrace error, the one-dimensional radius of curvature of the spherical mirror is 0.04% and the one-dimensional radius of curvature is 0.5% contrast with profilometer measurement results.