| 摘要 |
PROBLEM TO BE SOLVED: To obtain rigid and stable constitution with a large numerical aperture, a large image plane, and sufficient laser bandwidth by forming <=4 lenses of a 2nd material. SOLUTION: All lenses in a double-path area of the catadioptric optical system CS are combined with a single lens group which is contiguous to a concave mirror 411. This lens group includes positive lenses 403 and 404 and three negative lenses 405 and 410. When negative lenses like those are changed in number from two to three, the beam angle increases more smoothly and correction is optimized to simplify the structure of the lens barrel of the catadioptric optical system CS. The lenses 403 to 410 and mirror 411 are refraction projection exposure lenses and can be fitted to a small-sized unit. In this case, the positive lenses 403 and 404 are made of fluorite (having a diameter of, e.g. 200 mm) and, therefore, assists achromatization. Here, it is important that excellent achromatization is performed by up to three to four lenses in total.
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