| 摘要 |
PROBLEM TO BE SOLVED: To correct the gradient as to the intensity generated along a circumferential diction in a diffraction ring which is to appear in the vicinity of the periphery of a laser beam by rotating at least one lens which is included in an optical system around an axis whose direction is different from that of the optical axis of the lens. SOLUTION: A lens 20 whose optical axis coincides with the center axis in a design of an optical system is irradiated with a laser beam. Then, side robes are generated near by both hems of a curve indicating the intensity distribution of a final image. Next, a point at which side robes of both the left and the right become equal or they become the nearest to being equal is searched by changing the angle relation around the axis between a lens holder 21 and a lens holder 23 by rotating the lens holder 21 in a state in which bolts 24 are loosened. When the side robes become equal, peaks of the side robes become the lowest. That is, the gradient as to the intensity generated along the circumferential direction is corrected in the diffraction ring which is to appear in the vicinity of the periphery of the final image and the maximum intensity of the diffraction ring can be made small.
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