Patent ID: 6124924
Filing Date: 2000-09-26
Classification: G02B,G03F,G11B

Abstract:
An optical apparatus for maintaining a desired position of an article, the apparatus comprising:(a) an illumination unit generating a light beam for illuminating an elongated region of the article and producing light returned from the illuminated region;(b) a focusing optics for focusing the beam onto a focal plane and collecting at least a portion of the returned light;(c) a focus detection unit comprising an imaging optics and a detector, having a sensing surface responsive to light impinging thereon for generating data representative thereof, the imaging optics receiving at least a part of the collected returned light and forming first and second images on said sensing surface, wherein the first and second images are formed by first and second spatially separated substantially identical light components of the collected returned light, respectively, propagating symmetrically relative to an optical axis of said focusing optics, a position of the first image relative to the second image being indicative of the position of the article relative to the focal plane.