Converging light beam focus detector using two equally and oppositely offset light beam spot size detectors

摘要

Two spot size detecting elements are disposed on both sides of an effective scanning area on a scanning surface and spaced from the scanning surface perpendicularly in opposite directions by the same distance, and detect diameters of scanning laser beam. A comparison circuit compares the beam diameters as detected by the two spot size detecting elements. An electrostrictive element attached to a light source deformed in accordance with a comparison result to move the light source so as to correct a converging position of the scanning laser beam.