Development of high-accuracy profile measuring system for focusing mirror of SOR (Synchrotron Orbital Radiation)

Photon Factory needs a focusing mirror with high form accuracy of 0.01 μm/100 mm for utilizing SOR (Synchrotron Orbital Radiation). In order to finish a focusing mirror with such a high accuracy by NC EEM (Numerically Controlled Elastic Emission Machining), the measurement of the surface profile of preworked mirror should be made with enough accuracy. However, the measuring method or the measuring instrument with such a high accuracy of 0.01 μm/100 mm has not been developed yet. In the present study, the normal vectors at each points on the mirror surface are determined by making the incident light beam on the mirror surface and the reflected beam at that point coincident, the surface gradients at each points are calculated from the normal vector and the surface profile is obtained by integrating the gradients. The measuring instrument was constructed according to the above principle of measuring method. The surface profile of the mirror with the size of 100 mm square and with the radius of curvature of 5 550 mm was measured by the present instrument with the accuracy of 0.01 μm/100 mm.