Alignment technology for double-fiber phase-shifting point diffraction interferometer

In order to measure the wavefront aberration of the EUVL objective system with the super high accuracy, the double-fiber phase-shifting point diffraction interferometer was introduced, its working principle was introduced, and the adjustment scheme of interferometer was designed critically. All the components were positioned accurately, the test beam and reference beam were ensured to be strictly vertical, the maximum coupling efficiency between the coupling system and optical fiber and maximum fringe contrast were realized, which provided preparation for ultimately ultra high precision test of the wavefront aberration of EUVL objective system. After the alignment was completed, an optical system was measured by the experimental device, the tested optical system wavefront aberration was restored by the 13-frame phase-shifting algorithm, the good results were obtained. The results are: PV value is 37.82 nm, RMS value is 7.83 nm.