Apparatus is disclosed for producing clock signals which are used to precisely control the modulation of a first light beam as it is line scanned by a moving mirror. The apparatus employs a second beam of light which is reflected from the moving mirror and is intensity modulated by a grating. A paraboloid...http://www.google.de/patents/US4616132?utm_source=gb-gplus-sharePatent US4616132 - Synchronization apparatus for scanner
