GB1531744A - Optical scanning system - Google Patents

Abstract

1531744 Optical scanning systems XEROX CORP 15 Oct 1975 [21 Nov 1974 (2)] 42256/75 Heading G2J [Also in Division H4] A flying spot scanning system comprises a laser for providing a beam 3 of light, a lens for imaging said beam to a spot in a focal plane, a scanner 10 for directing said beam through a predetermined scan angle where said spot traverses a focal arc, and optical means between the scanner and said focal arc for redirecting the beam such that the effective scan angle is smaller than said predetermined angle. The optical means consist of mirrors a, b, c, d disposed symmetrically about a line CL which bisects said predetermined scan angle, said mirrors redirecting said beam to provide two contiguous focal circles. In a modification each mirror has two facets to provide four focal circles. Instead of using mirrors, the optical means may consist of prisms (14), (16), Fig. 6 (not shown), the beam 3 being redirected from the reflective surfaces of the prisms. The prisms may be joined at an edge e, whereby two focal circles are produced, or they may be separated, Fig. 7 (not shown), whereby the focal circles (1), (3) corresponding to the prisms are separated by a third focal circle (2) through which the spot is scanned by scanner 10. Glass plates (22), (24) are located, one between a respective prism and the focal plane, such that the focal object planes corresponding to the prisms and scanner 10 alone are coincident. A filter (28) of neutral density is disposed between scanner 10 and focal circle (2) to match the intensity of the beam 3 which is directed by scanner 10 in relation to focal circle (2) with the beams directed through the prisms to focal circles (1), (3). If beam 3 consists of polarized light, filter (28) may be a polarizer. The system may be used in a "read" mode when an original picture or document is scanned to determine the reflected or transmitted intensity, or in a "write" mode wherein the beam is modulated and scanned across a photo-sensitive medium. The scanner may be an acousto-optical deflector, a scanning polygon, or a galvanometer. The light may be modulated by a Pockel's cell. For an infrared illumination, a thin layer of gold is used to provide the mirrored surfaces.