A method and apparatus for highly efficient use of higher-order diffraction beam in holography. The thermoplastic hologram (10) is recorded at a recording angle (.theta..sub.R) between two coherent beams (12, 14) equal to a first-order diffraction angle (.theta..sub.1) corresponding to the angle (.theta..sub.2) of the desired higher-order beam (18) set to the angular peak (22) of diffraction efficiency (20) of the material of the hologram. On read-out, the desired higher-order beam is read. By use of the invention, the intensity of a higher-order beam can be tuned and made nearly equal to that of the first-order beam. Thereby, useful non-linear holographic systems, such as an associative memory (FIG. 4), can be practically implemented.
A system for reading and writing indicia on a medium including a light source for producing a light beam; a reading element for directing the light beam at the medium so as to scan indicia disposed on a first portion of said medium, detecting at least a portion of the light of variable intensity reflected off the indicia, and generating an electrical signal indicative of the detected light intensity; and a writing element for directing the light beam at the medium in a pattern on a second portion of the medium so as record information on the medium. The light beam is preferably a laser beam generated by a semiconductor laser, and a mirror is used to scan the beam both for reading and writing.
A record carrier (e.g., an identification card) of the type containing machine-readable representations of data, wherein the record carrier comprises a substrate, a first pattern of machine-readable indicia applied to one surface of the substrate, and a hologram containing machine-readable data disposed on one surface of the substrate. The information represented by the machine-readable indicia and the machine-readable data are related to one another so as to enable a user to verify the authenticity of the record carrier by comparison of the indicia and the data.
A miniature module emits and focuses a divergent light beam. The focusing module consists of a small-sized light emitter, such as a laser diode, and a micro-optical element seated in a lens holder. The outside diameter of the micro-optical element is 4 mm or less and preferably less than or equal to 2.5 mm. The micro-optical element may be a small conventional lens, a gradient index lens, or one of several types of diffractive optical element. The focal length of the module relative to the light from the emitter is set by sliding the lens holder along its central axis and permanently adhering it in place with respect to the emitter after focusing. During focal adjustment, axial rotation between the lens holder and between the base of the emitter is prevented by a series of notches. The miniature focusing module is smaller, lighter, costs less and may provide a larger relative aperture than the conventional structures currently used for example in solid state laser scanners.
A system for reading and writing indicia on a medium including a light source for producing a light beam; a reading element for directing the light beam at the medium so as to scan indicia disposed on a first portion of said medium, detecting at least a portion of the light of variable intensity reflected off the indicia, and generating an electrical signal indicative of the detected light intensity; and a writing element for directing the light beam at the medium in a pattern on a second portion of the medium so as record information on the medium. The light beam is preferably a laser beam generated by a semiconductor laser, and a mirror is used to scan the beam both for reading and writing.
A system for reading and writing indicia on a medium including a light source for producing a light beam; a reading element for directing the light beam at the medium so as to scan indicia disposed on a first portion of said medium, detecting at least a portion of the light of variable intensity reflected off the indicia, and generating an electrical signal indicative of the detected light intensity; and a writing element for directing the light beam at the medium in a pattern on a second portion of the medium so as record information on the medium. The light beam is preferably a laser beam generated by a semiconductor laser, and a mirror is used to scan the beam both for reading and writing.
