Method for using a deep image hologram as a security device and a deep image hologram
AssigneeE. I. Du Pont de Nemours and Company
InventorsWilliam Molteni, Michael Fickes
Life of this patent
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Abstract
A holographic optical element (HOE) that is comprised of a deep image hologram and a method for using this HOE as a security device are described. The deep image hologram is viewable with a collimated or at least partially collimated light source having a center wavelength in the visible region of the electromagnetic spectrum and a spectral bandwidth, wherein the spectral bandwidth of the collimated or at least partially collimated light source at least partially overlaps the spectral bandwidth of the deep image hologram. The deep image hologram is not viewable (i.e., appears essentially unrecognizable to the human eye) with a diffuse lighting source, such as ordinary room lighting.
Claims10
A method for viewing a reconstructed image of a deep image hologram contained within a holographic optical element having a surface, said method comprising:
- providing a deep image hologram which is a substantial distance from the surface of the holographic optical element wherein the deep image hologram appears unrecognizable to the human eye under diffuse lighting sources;
- and
- illuminating the image with at least a partially collimated light source having a spectral bandwidth that at least partially overlaps that spectral bandwidth of the deep image hologram wherein the image is resolved.
A method for establishing the authenticity of an article containing a holographic optical element comprising a deep image hologram having a surface, said method comprising the steps of:
- (a) providing a holographic optical element on an article to be authenticated, said holographic optical element comprising a deep image hologram having a surface, wherein the deep image hologram is located at a substantial distance from the surface of the holographic optical element, whereby the deep image hologram appears unrecognizable to the human eye under diffuse lighting sources;
- (b) illuminating the image with at least a partially collimated light source having a center wavelength in the visible region of the electromagnetic spectrum and a spectral bandwidth, wherein the spectral bandwidth of the at least partially collimated light source at least partially overlaps the spectral bandwidth of the deep image hologram;
- and
- (c) establishing the article bearing the holographic optical element to be authentic only if the deep image hologram is observable upon illumination with the light source in step (b) positioned at least one angle θ with respect to a normal line to the surface of the holographic optical element.
A method for making a master hologram comprising at least one deep image hologram, the method comprising the steps of:
- a. obtaining a model of all element(s) that are to be in the master hologram, the element(s) comprising at least one deep image hologram;
- b. placing a first photosensitive film suitable for holographic recording between the model and a coherent light source, the first photosensitive film having a surface;
- c. exposing the first photosensitive film with light from the coherent light source to record a first holographic image (H1) of the physical model, the first holographic image comprising at least one deep image hologram;
- d. inverting the first holographic image and removing the physical model;
- e. placing a second photosensitive film suitable for holographic recording between the coherent light source and the first holographic image, the second photosensitive film being proximate to the first holographic image;
- and
- f. exposing the second photosensitive film with light from the coherent light source to record a second holographic image (H2) as the master hologram, the second holographic image comprising at least one deep image hologram.
A deep image hologram contained within a holographic optical element having a surface, said image comprising:
- a hologram which is a substantial distance from the surface of the holographic optical element wherein the hologram appears unrecognizable to the human eye under a diffuse lighting source and recognizable under at least a partially collimated lighting source.
Dependencies are inferred from the claim text.