학술논문
Optical path length compensating optical system in an alignment apparatus
Document Type
Patent
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Abstract
An optical path length compensating device comprises a first objective having one focus coincident with a two-dimensional plane and provided for movement along the two-dimensional plane, a second objective having one focus coincident with a predetermined focal plane, first and second reflecting means provided in the optical path between the first objective and the second objective for movement along the optical path, the first reflecting means including at least one reflecting surface for turning the optical path from the first objective by a predetermined angle in a plane parallel to the two-dimensional plane, the second reflecting means including at least one pair of reflecting surfaces for directing the light from the first reflecting means to the second objective, means for moving the first objective and the first reflecting means in operative association with each other, and means for moving the second reflecting means so that the other focus of the first objective and the other focus of the second objective are coincident with each other.