Measuring the radius of curvature of a spherical mirror with an interferometer and a laser tracker

We present a method to accurately measure the radius of curvature of a concave spherical mirror with a phase-measuring interferometer and a laser tracker. Use of a laser tracker eases the alignment of the testing system, eliminates the need to move the test piece during the measurement, and improves the accuracy of the distance measurement. Using this method, we measured the radius of curvature of a spherical mirror 0.5 m in diameter and about 2.5 m in radius of curvature. The accuracy of the measurement is better than ±20 μm.