Diffraction grating

Patent Pending PROBLEM TO BE SOLVED: To solve a problem concerning cost and evaluation time of the conventional technology by measuring the diffraction light wavefront from the entire surface of diffraction grating and applying arithmetic processing to the obtained wavefront information. ; SOLUTION: Lights are applied to the entire surface of mono-axis diffraction grating 10 or bi-axis diffraction grating, and the respective wavefront information of plus first-order diffracted light and minus first-order diffracted light is evaluated by a shape measuring interferometer such as Fizeau type interferometer 11 or the like.