Detection of Imperfections on a Reflective Surface by Schlieren Illumination
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Imperfections and/or contaminants on a reflective surface are detected by a Schlieren optical illumination system. In Fig. 1, the rigid disk 1 is illuminated by light from a laser source 3, via a beam expander 5 and a first collimating lens 7. The incident light rays are reflected as shown schematically, and the reflected light is supplied to a vidicon detector 9, via a second collimating lens 11, an opaque optical stop element 13, located at the prime focus of lens 11, and an objective lens 15 focussed on the disk surface. With no imperfections on the surface of disk 1, no image is formed on the vidicon. With any imperfection, light is diffracted past the stop 13, and is imaged as a bright line or bright points on the surface of the vidicon, contrasted with a dark background field.