Technique for recording a hologram suitable for use in optical retrieval system

In a hologram recording system for recording an interference pattern having Fresnel properties in at least one of two orthogonal directions, on a recording medium with two angularly displaced interfering beams of coherent energy of a first given wavelength .lambda..sub.1 to produce a certain type of hologram, said certain type of hologram being responsive on readout to the illumination thereof with a plane wave of coherent wave energy of a second given wavelength .lambda..sub.2 which is oriented substantially normal to the plane of said hologram for diffractively deriving an output beam of coherent wave energy which coverges in at least said one of said two orthogonal directions and which has a crossover spaced a preselected distance Z.sub.3 from the plane of said hologram;

• said hologram recording system comprising:
• coherent wave energy translation means for simultaneously illuminating an area of said recording medium with (1) a first incident beam of said .lambda..sub.1 coherent wave energy which diverges in at least said one of said two orthogonal directions from a first predetermined crossover spaced a distance substantially equal to Z.sub.1 from the plane of said recording medium and (2) a second incident beam of said .lambda..sub.1 wavelength coherent wave energy which diverges in at least said one of said two orthogonal directions from a second predetermined crossover spaced a distance substantially equal to Z.sub.2 from the plane of said recording medium, and
• wherein the respective values of distances Z.sub.1 and Z.sub.2 are related to the preselected distance Z.sub.3 substantially in accordance with the following equations:
• ##EQU2## where .alpha. is equal to the ratio of .lambda..sub.2 to .lambda..sub.1.