PHOTOELECTRIC SYSTEM AND METHOD FOR DETECTING THE LONGITUDINAL LOCATION OF SURFACES

摘要

A method and an arrangement enabling the location of a plane or spherical, specularly reflecting or diffusing surface. The method comprises alternately modulating the "tube" or total length of the instrument in such a manner as to create a focusing error alternating with respect to that plane of the image which would correspond to perfect focus without modulation a variable photoelectric signal is provided by a photoreceiver which is subject to variations in light flux transmitted by an interferogram disposed in the portion common to the two waves in the plane of the pupil. An error signal produced by the treatment of the photoelectric signal is used to control the displacement of the objective or the object along the optical axis in order to focus or calculate the focusing error. The method and arrangement are useful especially in the field of metrology.