Abstract:
Interfering radiations of substantially coherent electromagnetic radiation of a wave length within a range to which a layer of photochromic material is sensitive are transmitted in different directions through a layer of the material in selected regions. The interfering radiations in each region produce antinodes which form peak energy levels to sensitize the photochromic material in spaced, parallel surfaces of a periodic structure having altered transmission and reflective properties. The sensitized regions constituting the recorded information may be read by radiation of a lower energy level or of a wave length outside the range of sensitivity directed to the regions, the reflected radiation being detected to represent the recorded information. A plurality of interfering beams may be transmitted in different directions in the same region to produce different recordings and may be detected by the same radiations. The photochromic material may be restored to its original state by radiation of a wave length in a third range, so that such radiation may be used to erase recording in any region.
Abstract:
Interference pattern recording of large objects or scenes having dimensions exceeding the coherence lengths of available light sources is accomplished. The recording is performed by illuminating the storage medium with a plurality of reference beams all of which are collinear and the scattered radiation from the object. A path length difference not exceeding and preferably slightly less than the coherence length of the radiation sources is introduced into each successive reference beam.
Abstract:
1,160,048. Read-only stores. INTERNATIONAL BUSINESS MACHINES CORP. 28 May, 1968 [14 July, 1967], No. 25424/68. Heading G4A. A data store uses an interference pattern, data being distinguished by bandwidth. An optical read-only store uses a Lippmann photographic plate in the thickness of which spaced reflecting layers have been established by setting up standing waves of light, developing and fixing. An electro-optical digital light deflector is used for selecting a storage position at which a 5-bit word is recorded using wide and narrow ranges of wavelengths (centred on the same wavelength) for bit-values 0 and 1 respectively, the ranges relating to different bit positions being non-overlapping in the frequency spectrum. A shutter, and rotatable disc bearing 5 x 2 bandpass filters, are used in recording. On read-out, a Fabry-Perot multibandpass filter (two spaced partially-reflecting films) passes a range of wavelengths (of light reflected from the photographic plate) at each bit position in the frequency spectrum which includes part of the " 0 " range but essentially none of the "1" range, a prism then frequencyanalysing the light on to a line of five photocells. Alternatively, for read-out, a Michelson interferometer produces interference fringes from essentially only the "1" bits, by suitable choice of the path-difference in the interferometer. The fringes are diffused by a groundglass screen and then frequency-analysed by a lens system on to a line of five photo-cells. Use of holography and Lippmann holography are mentioned as alternatives.
Abstract:
1,107,477. Information recording. INTERNATIONAL BUSINESS MACHINES CORPORATION. Sept.13, 1966 [Dec.30, 1965], No.40764/66. Heading G2J. Light from a laser 1 passes through a film 3 having a photo-sensitive emulsion 4, e. g. a silver halide emulsion, and is reflected back upon itself by a mirror 2, thereby causing the light-waves to pass again through the film and set up standing waves therein, giving rise to equispaced parallel layers of metallic silver, as in the Lippmann process. The film is mounted so as to be rotatable into different angular positions, thus the light-waves form groups of spaced layers, the layers of each group being inclined to the layers of every other group. Alternatively, the film 3 may be exposed to light of different wave-lengths at different angles, or to light of different wave lengths at the same angle. To record information in binary form, the radiation from an He-Ne laser is used to form periodic structures, as described, in each region of the film, each structure representing one bit of information in one region. The information recorded in the film is read by transmitting radiation of the appropriate wave-length through the film, and sensing the transmitted or reflected wave energy as modified by the periodic structure of the film.