Method for using a deep image hologram as a security device and a deep image hologram
A holographic optical element (HOE) that includes 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.
1. A method for viewing a three-dimensional image comprising the steps of:
a) providing a surface image from a surface hologram wherein the surface image is visible in diffuse room light;
b) providing a deep image from a deep hologram, the deep hologram comprising a surface and a spectral bandwidth, wherein the deep image is a distance from the surface of the deep hologram such that the deep image appears unrecognizable to the human eye under diffuse light; and
c) illuminating the deep hologram with at least partially collimated, incoherent light from a light source having a spectral bandwidth that overlaps the spectral bandwidth of the deep image hologram so as to make the deep image recognizable to the human eye.
2. The method of claim 1 wherein the deep hologram is formed by a volume reflection method.
3. A three dimensional image comprising a surface image visible in diffuse room light from a surface hologram and a deep image from a deep hologram, wherein the deep image is located a distance from the surface of the deep hologram and appears unrecognizable to the human eye under diffuse light but is visible to the human eye when the deep hologram is illuminated with at least partially collimated, incoherent light from a light source having a spectral bandwidth that overlaps the spectral bandwidth of the deep hologram.
4. The three dimensional image of claim 3 wherein the deep image is located at a distance of at least ⅛ inch from the surface of the deep hologram.
5. The three dimensional image of claim 3 wherein at least one angle θ with respect to a normal line to the surface of the deep hologram is in the range from about +55 degrees to about −55 degrees including all degrees contained therein.
6. A method for establishing the authenticity of an article comprising the steps of:
(a) providing the three dimensional image of claim 3 on an article; and
(b) authenticating the article upon illumination of the three dimensional image with at least a partially collimated, incoherent light from a light source having a spectral bandwidth that overlaps the spectral bandwidth of the deep hologram and visualizing the deep image.
7. A device comprising a deep hologram comprising a surface and a spectral bandwidth and a surface hologram producing a three dimensional image comprising a surface image visible in diffuse room light from the surface hologram and a deep image from the deep hologram, wherein the deep image is located a distance from the surface of the deep hologram such that the deep image appears unrecognizable to the human eye under diffuse light but is visible to the human eye when the deep hologram is illuminated with at least partially collimated, incoherent light from a light source having a spectral bandwidth that overlaps the spectral bandwidth of the deep hologram.
8. A method for establishing the authenticity of an article comprising the steps of:
(a) providing a device of claim 7 on an article; and
(b) authenticating the article upon illumination of the three dimensional image with at least a partially collimated, incoherent light from a light source having a spectral bandwidth that overlaps the spectral bandwidth of the deep hologram and visualizing the deep image.