Patent ID: 8553232
Filing Date: 2013-10-08
Classification: G01B

Abstract:
1. An interference objective lens unit, comprising: an objective lens that causes light emitted from a light source to converge on a measuring object; a beam splitter that is provided closer to the measuring object than the objective lens, that splits the light transmitted through the objective lens into a reference optical path in which a reference mirror is provided and a measuring optical path in which the measuring object is placed, and that superposes reflected light from the reference mirror and reflected light from the measuring object to output interference light; a first holder that holds the objective lens and that is formed by material having a first linear expansion coefficient, the first holder holding the objective lens by contacting the objective lens; and a second holder that holds a plate having the reference mirror by contacting the plate, the second holder formed by material having a second linear expansion coefficient which is different from the first linear expansion coefficient, wherein when a usage environment temperature changes, a difference in the linear expansion coefficients between the first holder and the second holder corrects an optical path difference between the reference optical path and the measuring optical path.