| 摘要 |
PROBLEM TO BE SOLVED: To reduce the intensity distribution fluctuation of a laser beam and to thereby propagate it with a uniform intensity distribution even for a long distance, by outputting a laser beam having a flat-top intensity distribution while forming the laser beam into a form in which the phases of the wave fronts at both ends of the laser beam are retarded. SOLUTION: A laser beam having a flat-top intensity distribution outputted from a laser device 10 is made incident on an up-collimator 2 via a refracting medium 11. Here, when the laser beam passes through the medium 11, the thickness of a glass material constituting the medium 11 is made different by 1.2μm between a portion through which the central portion of the laser beam passes and a portion through which both end portions of the laser beam pass, so that the medium 11 generates an optical path difference of 600 nm between the central portion and both end portions of the laser beam. As a result, the laser beam has wave fronts whose phase is 600 nm behind as a wavelengthλat its end portions when passing through both ends of the medium 11, both ends being equal to a distance of 1 mm.
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