| 摘要 |
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. The diffraction grating is relatively inclined to the shape measuring interferometer so that the plus first-order diffracted light or minus first-order diffracted light from the diffraction grating and reference light from a reference optical flat 12 provided inside the Fizeau type interferometer 12 may be overlapped. The Fizeau type interferometer 12 can measure the wavefront from the entire surface of the diffracted light at the same time and in a short time. The obtained wavefront of the plus first-order diffracted light or minus first-order diffracted light is subtracted to find out the variation of pitch over the entire surface of the diffraction grating. COPYRIGHT: (C)2011,JPO&INPIT
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