| 摘要 |
PROBLEM TO BE SOLVED: To enable to output a light of high monochromaticity in a set wavelength range with high intensity, irrespective of a set wavelength. SOLUTION: An image of an entrance slit 21 is formed on an exit slit 25 with image forming optical systems 22, 24. Out of the images formed on the exit slit 25, slit width w1 of the entrance slit 21 and slit width w2 of the exit slit 25 which makes width of an image of monochromatic light of a central wavelength which image is to be outputted from the exit slit 25 coincide with slit width of the exit slit 25 are obtained by operation with a control part. Slit width driving parts 26, 27 adjust the width of the entrance slit and the width of the exit slit to w1 and w2.
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