JPH10143057A - Complex hologram - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a complex hologram of which image is clearly reproducible with while ligth even by using a transmissible hologram, and wich cannot be copied. SOLUTION: A mirror reflection type Lippmann hologram 3 is formed by being stacked on the back of a transmissive hologram 1 such as an image hologram, etc., and when reproducing the transmissible hologram 1 with white light 6, light except that of intrinsic reproducing wave-length λ0 passed the Lippmann hologram 3 on the back and does not diffract on the front surface, but only the light of the reproducing wave-length λ0 is diffracted by the transmissible hologram 1 and Lippmann hologram 3 and comes out on the front surface, therefore, a phenomenon in which reproduced image position differs from wavelength to wavelength does not take place but a mirror image of an objective to be picked up can clearly be reproduced even by irradiating with white light 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite hologram, and more particularly to a composite hologram suitable for use as an anti-duplication hologram which is attached to an identification card or the like and used for enhancing security.

[0002]

2. Description of the Related Art Conventionally, in order to ensure that a CD card, a prepaid card, a commuter pass, a passbook, a passport, an identification card, a product, and the like are true and not forged, a three-dimensional image, a pattern, and the like are used. 2. Description of the Related Art Affixing a label, a seal, or the like made of a recorded relief hologram or Lippmann hologram to an object is widely performed.

[0003]

These holograms can be reproduced by simple reproduction illumination light or white light, and it is not always difficult to forge such a hologram by a method such as duplication. Therefore, the security of labels, seals, and the like made of such holograms is not always high.

[0004] Conventionally, transmission holograms that can be reproduced by white light include, for example, image holograms,
Rainbow holograms and the like are known (for example, Masane Suzuki, "Practical holography technology supplemented and revised edition")
(Optronics), especially image holograms, where the reproduction position of the reconstructed image differs depending on the wavelength of the reconstructed illumination light, it is actually difficult to clearly reproduce the image with white light. It could not be used to ensure sex.

The present invention has been made in view of such problems of the prior art, and it is an object of the present invention to enable clear image reproduction by white light even when a transmission hologram is used, and to reproduce images. It is to provide an impossible composite hologram.

[0006]

According to the present invention, there is provided a composite hologram comprising a transmission type hologram and a specular reflection type Lippmann hologram laminated on a back surface thereof.

In this case, examples of the transmission hologram include an image hologram and a rainbow hologram.

It is desirable to provide a light absorption layer on the back surface of the specular reflection type Lippmann hologram.

Further, an off-axis specular reflection type Lippmann hologram may be used as the specular reflection type Lippmann hologram.

Further, the specular reflection type Lippmann hologram may have a distribution of wavelengths satisfying the diffraction condition in the plane.

In the above-mentioned present invention, since the specular reflection type Lippmann hologram is laminated on the rear surface of the transmission type hologram, when the transmission type hologram is reproduced with white light, light other than the original reproduction wavelength is applied to the rear surface. Only the light of the reproduction wavelength is diffracted by the transmission hologram and the Lippmann hologram to the front without being transmitted through the Lippmann hologram and diffracted to the front, so that the position of the reproduced image does not differ for each wavelength and is white. The mirror image of the subject can be clearly reproduced even when irradiated with light. Further, when a hologram having substantially the same characteristics as the composite hologram is obtained by duplication, the hologram has a structure that can be easily distinguished from the composite hologram of the present invention. It is suitable for a hologram for preventing forgery of a book or the like.

[0012]

Next, an embodiment of the composite hologram of the present invention will be described. First, an image hologram, which is one of the transmission holograms, will be described with reference to FIG. 3 (Masane Suzuki, “Practical holographic technology augmented and revised edition”, Optronics Co., Ltd.). First, FIG.
As shown in FIG. 5, a hologram dry plate 21 such as a silver halide film is arranged at a distance from the subject S, the subject S is illuminated by the illumination light 22, and object light 23 scattered from the hologram dry plate 21 is incident on the hologram dry plate 21. A reference hologram 24 branched from the light 22 is incident from the same side as the object light 23, and the object light 23 and the reference light 24 are interference-recorded in the hologram dry plate 21, thereby producing a master hologram 25.

Next, as shown in FIG. 3 (b), the master hologram 25 is provided with a reference beam 2 at the time of recording.
When the reproduction illumination light 26 having the same wavelength (conjugated) that travels in the opposite direction to the reproduction light 4 is emitted, the reproduction light 27 diffracted therefrom forms the real image S ′ at the original position of the subject S, but the real image S ′
, Another hologram dry plate 29 is arranged in the vicinity, and at the same time, the reference light 28 branched from the reproduction illumination light 26 is made incident from the same side as the reproduction light 27, and the reproduction light 27 and the reference light 28 interfere in the hologram dry plate 29. By recording, the image hologram 30 is produced.

When the image hologram 30 thus manufactured is irradiated with light having the same wavelength conjugate with the reference light 28 or white light 31, as shown in FIG.
The image hologram 30 is reproduced by the reproduced light 32.
Is reproduced in the vicinity of the original image S ″ of the subject S.

The principle of the image hologram, which is one of the transmission holograms, has been described above. When the hologram is to be reproduced with white light, the position of the reproduced image actually differs for each wavelength. It is difficult to clearly reproduce the image of the subject.

Accordingly, in the present invention, as shown in the cross section in FIG. 1, an image hologram 1 which is a transmission hologram as described above, and an interference fringe 4 formed below the image hologram 1 in parallel with the plane of the film. A mirror reflection type Lippmann hologram 3 is superimposed, and a light absorbing layer 5 is provided on the back surface of the Lippmann hologram 3 to form a composite hologram 10 of the present invention. In FIG. 1, reference numeral 2 denotes an image hologram 1
Relief surface.

Here, a specular reflection type Lippmann hologram 3 in which interference fringes 4 are formed parallel to the plane of the film.
For example, as shown in FIG. 2, a reflective layer 12 is disposed on the back surface of a photosensitive material 11 for a volume phase hologram having a large thickness such as a photopolymer, and parallel coherent light 13 having a specific wavelength is emitted from the front surface side. The light enters the photosensitive material 11 and passes through the reflective layer 12.
In this case, the light 14 and the incident light 13 reflected by the light source can interfere with each other in the photosensitive material 11 so that they can be easily manufactured.

[0018] Since the composite hologram 10 of the present invention are configured as described above, as shown in FIG. 1, is irradiated with white light 6 images hologram 1 for reproduction of the original with relief surface 2 reproduction wavelength lambda ₀ of wavelength λ ₁ of the non-light 7 _0, λ _2, ·
... light 7 _1, 7 _2, ... is also diffracted at the same time the transmission direction at different diffraction angles. However, Lippman hologram 3
Since there is a wavelength selective, light 7 diffracted wavelength lambda _{0 0}
If There Oke constitute a Lippmann hologram 3 to diffract satisfies the diffraction condition (Bragg condition), the light 7 ₀ of the wavelength lambda ₀ is diffracted in the direction of regular reflection, to answer the reflection direction from the composite hologram 10 Become. Other wavelengths λ ₁ , λ
_2, the light 7 ₁ ..., 7 _2, ... it is absorbed by the back surface of the light absorbing layer 5 in direct without being diffracted by the Lippmann hologram 3. Therefore, since only the light 7 ₀ of the wavelength lambda ₀ in the white light 6 is diffracted from the image hologram 1, different phenomena for each wavelength the position of the image to be reproduced does not occur, even if irradiated with white light object Mirror image can be clearly reproduced.

The specular reflection type Lippmann hologram 3
When using an off-axis specular reflection type Lippmann hologram in which fine mutually parallel interference fringes 4 are not parallel to the plane of the film but are inclined with respect to the film surface, the original light 7 of the reproduction wavelength λ _{0 0}
Light 7 _{1 of} wavelengths λ ₁ , λ ₂ ,.
7 _2, even ... is reflected by the back surface of mirror reflection type Lippmann hologram 3, the light 7 ₀ of the wavelength lambda ₀ is diffracted are separated in a direction different from the those of the reflection direction, light Even if the absorption layer 5 is not provided, a mirror image of the subject can be clearly reproduced even by irradiation with white light.

Now, let us consider copying the composite hologram 10 as described above. As shown in FIG. 4, a hologram photosensitive material 35 having a large thickness such as a photopolymer is brought into contact with or brought close to the composite hologram 10, and is overlaid.
When the coherent light 36 for copying is incident from the photosensitive material 35 side from the same direction as the light 6 for reproducing the image hologram 1, the light transmitted through the photosensitive material 35 reaches the composite hologram 10 and has the above-described wavelength. The light 37 (= 7 ₀ ) of λ ₀ is diffracted in the reflection direction. Therefore, by causing the incident light 36 and the reflected diffracted light 37 to interfere with each other in the photosensitive material 11, the composite hologram 10 can be duplicated to produce a Lippmann hologram having substantially the same function as the composite hologram. But,
The hologram is analyzed microscopically, and it can be immediately recognized that the hologram is composed of a Lippmann hologram alone and does not include a transmission hologram, so that the hologram can be determined to be a forgery.

Incidentally, a photopolymer has recently been used as a recording material for a Lippmann hologram or a volume hologram. The diffraction wavelength characteristic of a volume phase hologram recorded in a photopolymer by two-beam interference is narrow. Therefore, it is known to use a color tuning technique on the hologram after the interference recording in order to widen the diffraction wavelength characteristic (Japanese Patent Laid-Open No. 3-4).
No. 6687).

In this color tuning, a color tuning film is brought into close contact with a photosensitive material such as a photopolymer on which a hologram is recorded and heated to diffuse a monomer, a plasticizer, and the like into the photosensitive material, thereby broadening the diffraction wavelength. Since the half value width of the diffraction wavelength increases, illuminating the Lippman hologram after color tuning with white light increases the diffracted light and improves the luminance. At the same time, such color tuning involves a phenomenon that the center diffraction wavelength shifts to a longer wavelength side.

Therefore, as the next embodiment of the present invention, as shown in FIG. 5, the above color tuning is performed only on a predetermined pattern area 38 of the specular reflection type Lippmann hologram 3 in the composite hologram 10, and keep changing the wavelength which satisfies the diffraction conditions of the region (Bragg condition) so that the lambda _{0 'from} lambda _0. Then, from this region 38 exiting the reflective direction is the wavelength lambda _{0 'light} 7 _0', is different from the other regions and the light 7 ₀ of the wavelength lambda ₀ is exiting the reflection direction, white light When irradiated, the composite hologram 10 of FIG.
From this, a mirror image of the subject is clearly reproduced in two different colors depending on the diffraction position.

When the composite hologram 10 shown in FIG. 5 is copied in the arrangement shown in FIG. 4, as long as the light 36 for copying has a single wavelength, no diffracted light is generated from the area 38 in the reflection direction. In this case, forgery is difficult because a Lippmann hologram having substantially the same effect as that of the composite hologram 10 cannot be reproduced.

Although the composite hologram of the present invention has been described based on several embodiments, the present invention is not limited to these embodiments, and various modifications are possible. For example, a rainbow hologram may be used instead of an image hologram as a transmission hologram forming a composite hologram. Further, as the transmission hologram, a phase hologram may be used instead of the relief hologram.

[0026]

As is apparent from the above description, according to the composite hologram of the present invention, since the specular reflection type Lippmann hologram is laminated on the back surface of the transmission hologram, the transmission hologram is reproduced with white light. In this case, light other than the original reproduction wavelength passes through the Lippmann hologram on the back side and does not diffract to the front, and only light of the reproduction wavelength is diffracted by the transmission hologram and the Lippmann hologram and exits to the front. The phenomenon that the position differs for each wavelength does not occur, and a mirror image of the subject can be clearly reproduced even when white light is irradiated. Further, when a hologram having substantially the same characteristics as the composite hologram is obtained by duplication, the hologram has a structure that can be easily distinguished from the composite hologram of the present invention. It is suitable for a hologram for preventing forgery of a book or the like.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a composite hologram according to the present invention.

FIG. 2 is a view for explaining a method of manufacturing a specular reflection type Lippmann hologram as a component of the composite hologram of FIG. 1;

FIG. 3 is a diagram for explaining the principle of an image hologram.

FIG. 4 is a view for explaining a method of copying the composite hologram of FIG. 1;

FIG. 5 is a sectional view of an embodiment of a composite hologram obtained by performing color tuning on a specular reflection type Lippmann hologram.

[Explanation of symbols]

S ... object S '... real S "... the image 1 ... image hologram 2 ... relief surface 3 ... mirror reflection type Lippmann hologram 4 ... interference fringes 5 ... white light 7 ₀ of the light absorbing layer 6 ... for reproduction of the object of the subject, 7 ₁ , 7 ₂ , 7 _{0 ′} Diffracted light 10 Composite hologram 11 Photosensitive material for volume phase hologram 12 Reflective layer 13 Coherent light 14 Reflected light 21 Hologram dry plate 22 Illumination light 23 Object light 24 Reference light 25 Master hologram 26 Reproduction illumination light 27 Reproduction light (diffraction light) 28 Reference light 29 Hologram dry plate 30 Image hologram 31 Reproduction illumination light 32 Reproduction light (diffraction light) 35 Volume-phase type Holographic photosensitive material 36 Coherent light for replication 37 Reflected diffracted light 38 Color-tuned pattern area

Claims (6)

[Claims] 1. A composite hologram comprising a transmission hologram and a specular reflection Lippmann hologram laminated on a back surface thereof. 2. The composite hologram according to claim 1, wherein said transmission hologram comprises an image hologram. 3. The composite hologram according to claim 1, wherein said transmission hologram is a rainbow hologram. 4. The composite hologram according to claim 1, wherein a light absorbing layer is provided on a back surface of the specular reflection type Lippmann hologram. 5. The composite hologram according to claim 1, wherein the specular reflection type Lippmann hologram is an off-axis specular reflection type Lippmann hologram. 6. The composite hologram according to claim 1, wherein the specular reflection type Lippmann hologram has a distribution at a wavelength satisfying a diffraction condition in the plane.