Patent GB-1082788-A (GB)
Title: Photo-recording apparatus
IPC: G11C13/04
Filed: 1966-05-24
Abstract: 1,082,788. Photo-recording apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 24, 1966 [June 21, 1965], No. 23102/66. Headings G2A, G2C and G2J. Photo-recording apparatus of the kind in which thin layers of reflecting material are formed in a photographic emulsion 1 by setting up a standing wave in the emulsion for each monochromatic light frequency, the emulsion being modified at the antinodes of the waves to produce light scattering layers spaced in depth at periodic intervals for each frequency present, is further provided with a variable optical mask 5 in the form of a photo-chromic member, and a mask control 6 capable of selectively subjecting areas of the mask to non-visible radiation to control areas of the mask capable of passing visible light, the mask and the control being positioned between the visible light source (not shown) and a reflective surface 3 of mercury used to set up the standing waves in the emulsion. The photo-chromic plate 5 is normally transparent but turns dark when subjected to ultraviolet light, and then becomes clear again when exposed to infrared radiation. The mask control 6 comprises a crystal 7 exhibiting the Kerr effect arranged between transparent electrodes 8 forming part of a circuit which, when a switch 11 is closed, will cause the crystal to rotate the plane of polarization of incident light through 90. Ultraviolet light polarized in a plane perpendicular to the drawing is deflected by a beam splitter 14 (which passes light polarized in the drawing plane) through the crystal 7 which, since the switch is closed, renders the ultraviolet radiation plane polarized in the drawing plane. This radiation now falls on the mask plate 5 which becomes opaque, and the radiation is blocked by an analyzer 18 which passes only light polarized in a plane perpendicular to the drawing plane. The switch 11 is opened and infrared light, polarized in the drawing plane, is directed to selected points on the plate 5 by a digital light deflector 20, and is then blocked by the analyzer 18. After the plate 5 has been made clear at all of the points at which the infrared beam was directed, information is written into the emulsion at corresponding points by directing light (28) of the selected frequency through the beam splitter (14) Fig. 3 (not shown), the light being polarized in a plane perpendicular to the drawing plane, and the switch 11 remaining open. The plate 5 may now be darkened again and infrared light directed on to areas on the plate where information corresponding to a different light frequency is to be written in the emulsion. After these areas are cleared, the emulsion is exposed to light of this different frequency. In another embodiment Figs. 4-6 (not shown) the plate (5) is provided with a mask (30) at its upper side, which mask passes light only at locations corresponding to those on the film (1) where information may be recorded. Ultraviolet light is directed at the openings in the mask corresponding to locations not required for a given frequency, thus darkening the plate below some openings (Fig. 4). The film is exposed (Fig. 5) and the darkened areas of the plate (5) cleared by exposure to infrared radiation (Fig. 6), switch (11) being closed for this last stage.