| 摘要 |
PROBLEM TO BE SOLVED: To measure the distance between a reflecting sample plane and a measuring apparatus having sensitivity range from a nanometer digit up to a subnanometer digit. SOLUTION: An orthogonal dual-frequency laser is used as a light source so as to constitute a heterodyne interferometer, light in one optical arm is condensed by a condensing lens to be image-formed on the reflecting sample plane, its reflected light and light in the other optical arm are overlapped by a divider and a polarizer, a plurality of photodetectors are placed in a plurality of places on the cross section of their overlapped luminous flux, and the phases of a plurality of heterodyne signals obtained by the plurality of photodetectors are obtained. By using the optical measuring apparatus, the position of the condensing lens is moved, in such a way that the obtained phases display a definite distribution, and the distance is measured precisely by a method, in which the approximate distance between the reflecting sample plane and the condensing lens is calculated, on the basis of its movement amount or in which the distance at a fine scale is calculated, on the basis of values of phase angles by the heterodyne signals.
|
