Security hologram, method of recording same, and method of using same
AssigneeE.I. du Pont de Nemours and Company
InventorSteven William MacMaster
Life of this patent
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Abstract
A security hologram is disclosed that is invisible to a human eye or to various optical detectors until the hologram is optically coupled to a suitable modifier (e.g., a prism). Also disclosed is a method of recording the security hologram and a method of using the hologram in security applications to establish authenticity of article(s).
Claims11
A security hologram comprising a covert holographic image that is invisible and not observable by a user in the absence of optical coupling of the hologram to an optical modifier but which may be made visible and observable by optical coupling of the hologram to the optical modifier during reconstruction of the image.
A method for making a security hologram comprising a covert image of an object, said method comprising the steps of:
- a) placing the object in contact with a first face of a prism, placing a first photosensitive film in contact with a second face of the prism, and holographically exposing the object, the prism and the first photosensitive film to a first coherent beam of electromagnetic radiation that is incident upon a third face of the prism wherein the first photosensitive film results in a first exposed photosensitive film having a H1 hologram of the object;
- b) curing the first exposed photosensitive film with electromagnetic radiation resulting in a first cured photosensitive film and removing the object from being proximate to the prism;
- and
- c) placing a second photosensitive film in contact with the first face of the prism, exposing the first cured photosensitive film, the prism and the second photosensitive film to a second coherent beam of electromagnetic radiation that is incident upon the third face of the prism wherein the second photosensitive film results in a second exposed photosensitive film having a H2 hologram, and curing the second photosensitive film with electromagnetic radiation resulting in a second cured photosensitive film.
A method for establishing the authenticity of an article containing a security hologram, said method comprising the steps of:
- (a) providing a security hologram on an article to be authenticated, the security hologram having a surface and comprising a covert image of at least one object, wherein the covert image appears invisible and unobservable by a user in the absence of optical coupling of the hologram to an optical modifier;
- (b) coupling an optical modifier to the surface of the security hologram;
- (c) illuminating the security hologram through the optical modifier with at least partially collimated light having a spectral bandwidth, wherein the spectral bandwidth of the at least partially collimated light overlaps the spectral bandwidth of the security hologram;
- and
- (d) establishing the article bearing the security hologram to be authentic when the covert image becomes observable upon illumination with the at least partially collimated light in step (c) with the light passing first through the prism and subsequently being incident upon the security hologram.
Dependencies are inferred from the claim text.