Surface gradient integrated profiler for x-ray and EUV optics: 3D mapping of 1m-long flat mirror and off-axis parabolic mirror

Abstract

A new ultra-precision profiler has been developed in order to measure such as asymmetric and aspheric profiles. In the present study, the normal vectors at each points on the surface are determined by the reflected light beam goes back exactly on the same path as the incident beam. The surface gradients at each point are calculated from the normal vector and the surface profile is obtained by integrating the gradient. The measuring instrument was designed according to the above principle of the measuring method. In the design, four ultra-precision goniometers were applied to the adjustment of the light axis for the normal vector measurement. The angle positioning resolution and accuracy of each goniometer are respectively 0.018 µrad and 0.2 µrad. In the measuring instrument, the most important item is the measuring accuracy of the normal vectors by the goniometers. Therefore, the rotating angle positioning errors were measured and calibrated. Then the measurement of a concave mirror with 300 mm radius and 460mm, 1m long plane mirrors were measured. Then, The 3D surface profile of the mirror such 1m-long flat mirror, a concave mirror with 2000 mm radius and off-axis parabolic mirror are obtained by integrating the interpolated gradient.