Hologram-writing apparatus providing precise tracking of a defocused write beam

Claim 1

Hologram-recording apparatus comprising a lens having a first focal point for a collimated light beam input and a second focal point for a diverging light beam input beyond said first focal point, a hologram-recording medium having its recording surface in a plane including said first focal point, an opaque plate located adjacent said recording surface having an aperture therein for defining information page locations on said surface, a data mask station positioned between said lens and said plate in which a plurality of data masks, each transmitting light in accordance with binary information stored therein, are individually and sequentially positioned, said lens and said plate being movable in identical parallel displacement, in planes perpendicular to the optical axis of said lens, with respect to said data mask station and said surface to a new position for each of said data masks, a source of coherent light, means for focusing said coherent light in a diverging beam on said lens; said data station, said recording surface, said source and said focusing means being fixed relative to each other along a common optical axis, and means for directing a reference light beam on said page locations on said recording surface.