Method for producing holographic optical element comprising primary and complementary holograms and associated methods for establishing authenticity of element used as security device
AssigneeE. I. Du Pont de Nemours and Company
InventorSylvia H Stevenson
Life of this patent
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Abstract
A method is provided for producing a holographic optical element that is comprised of at least one primary hologram (as defined herein) and at least one complementary hologram (as defined herein). The holographic optical element is useful as a security device, since it is relatively easily produced and yet is uncopyable in total. Also disclosed are methods for establishing the authenticity of the holographic optical element.
Claims12
A method for producing a volume holographic optical element useful as a security device comprising:
- (a) placing a photosensitive layer adjacent to a surface-relief hologram in a manner such that the photosensitive layer and the surface-relief hologram are in a relationship selected from the group consisting of 1) direct contact and 2) separated by one or more media with each medium having refractive index greater than 1;
- (b) exposing the photosensitive layer and the surface-relief hologram to a coherent light beam to record the surface-relief hologram in the photosensitive layer as reflection holograms comprising at least one primary hologram and at least one complementary hologram recorded by light diffracted from the surface-relief hologram;
- and
- (c) separating the surface-relief hologram from the imaged photosensitive layer to obtain the volume holographic optical element.
A method for establishing the authenticity of a holographic optical element comprising the steps of:
- (a) illuminating the holographic optical element with white light at an angle θ measured with respect to a normal line to a surface of the holographic optical element and simultaneously viewing the holographic optical element along the normal line to thereby see a holographic image having a first color, wherein |θ| is in the range of 15 degrees to 55 degrees;
- (b) illuminating the holographic optical element with white light at an angle δ=−θ±15° measured with respect to a normal line to a surface of the holographic optical element and simultaneously viewing the holographic optical element along the normal line to ascertain if a holographic image is observed having a second color that is characteristic of a wavelength that is longer than that for the first color;
- and
- (c) establishing the holographic optical element to be authentic only if a holographic image of the first color is observed in step (a) and a holographic image of the second color is observed in step (b).
A method for establishing the authenticity of a holographic optical element having a first surface, a second surface opposite the first surface, and a center plane that is parallel to at least one of the first and second surfaces and is located inside the holographic optical element such that equal portions of the holographic optical element lie on either side of the center plane, comprising the steps of:
- (a) illuminating the first surface of the holographic optical element with white light at an angle θ measured with respect to a normal line to the center plane of the holographic optical element and simultaneously viewing the first surface of the holographic optical element along the normal line to thereby see a holographic image having a first color, wherein |θ| is in the range of 15 to 55 degrees (°);
- (b) rotating the holographic optical element 180° about an axis in the center plane of the holographic optical element with continued illumination such that illumination from step (a) is now incident upon the second surface, and simultaneously viewing the second surface of the holographic optical element along the normal line to ascertain if a holographic image is observed having a second color that is characteristic of a wavelength that is longer than that for the first color;
- and
- (c) establishing the holographic optical element to be authentic only if a holographic image of the first color is observed in step (a) and a holographic image of the second color is observed in step (b).
Dependencies are inferred from the claim text.