| 摘要 |
PROBLEM TO BE SOLVED: To realize a new evaluation method, for a lens, as a substitute for a jitter method and a light intensity method by a method wherein light which is radiated from the lens is diffracted, beams of diffracted light at different orders are made to interfere, sharing interference light is obtained, the phase of the beams of diffracted light is changed and the phase of a change in light intensity is found in a plurality of measuring points on a sharing axis. SOLUTION: A laser beam 22 which is radiated from a laser generation source 21 is changed into parallel light 24 by a lens 23, and it is image-formed on a reflection-type diffraction grating 26 by an objective lens 25. A reflected laser beam 20 is reflected by a semitransparent mirror 27, and it is captured by an imaging element 28 so as to be processed by a signal processor 29. Then, in a region 34 in which zero-order diffracted light 31 and + first-order diffracted light 32 interfere, a change in terms of time in light intensity is measured in a point P1 and a point Pn which are at equal distance L from the center between the diffraction circle center O and the diffraction circle center O1 on a sharing axis which connects the diffraction circle center O of the zero-order diffracted light to the center O1 of the + first- order diffracted light. Then, the phase difference of a sine curve which expresses the change in the light intensity in the two points appears, and the characteristic (various aberrations) of the objective lens 25 is obtained on the basis of the phase difference.
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