Development of laser holographic anti-counterfeiting technology

After decades of development, laser holographic anti-counterfeiting products have gradually upgraded from the initial holographic anti-counterfeiting logo to the second generation, third generation and even fourth generation holographic anti-counterfeiting technology.

(I) the first generation of holographic anti-counterfeiting technology is laser embossed holographic image anti-counterfeiting.

Holography was discovered by American scientist Berg (MJ Buerger) when he took pictures of the atomic structure of crystals with X-rays, and established the holographic theory together with Gaber (D Gaber): using the principle of double-beam interference, the phase can be "combined" by making the object light and another beam (reference beam) coherent with the object light produce an interference pattern, thus, a holographic image can be obtained by simultaneously recording the lower phase and amplitude with a photosensitive negative. However, holograms are taken according to the principle of interferometry and must be recorded with high-density (resolution) photosensitive negatives. Due to the poor monochromaticity and poor coherence of ordinary light sources, the development of holographic technology is slow, and it is difficult to make a decent hologram. Until the emergence of laser in the early 1960 s, its high brightness, high monochromaticity and high coherence characteristics rapidly promoted the development of holographic technology. Many kinds of holograms were produced, and the holographic theory was well verified. However, due to the special requirements of shooting and reproduction, it has been almost confined to the laboratory since its birth.

In the late 1970 s, it was discovered that holograms have a surface structure that includes three-dimensional information (I. e., crisscrossed interference fringes), which can be transferred to materials such as high-density photosensitive negatives. In 1980, American scientists used imprint holographic technology to transfer the holographic surface structure to polyester film, thus successfully printing the world's first molded holographic picture. This kind of laser holographic picture is also called rainbow holographic picture. It makes the image on the plastic film through laser plate making, produces colorful diffraction effect, and makes the picture have two-dimensional and three-dimensional space sense, Under ordinary light, hidden images and information will be reproduced. When light shines from a certain angle, a new image will appear. This kind of embossed holographic picture can be copied in large quantities as quickly as printing, the cost is low, and it can be used in combination with various printing products. At this point, holography has taken a decisive step towards social applications.

Because the production technology of this embossed holographic picture was very advanced at that time, only a few people mastered it, so it was used as an anti-counterfeiting mark. The principle of its anti-counterfeiting is:

1. In the whole process of laser holographic picture shooting, if there is a different condition (such as the condition of shooting rainbow hologram), the effect of holographic logo will be different.

2. The holographic information of this holographic image cannot be photographed with ordinary photography, so the holographic pattern is difficult to be copied.

The first application of holographic images as anti-counterfeiting identification is JohnnyWalkeWhishy (a whiskey). When it was applied in Thailand, sales were said to have increased by about 45%.

Laser embossing holographic anti-counterfeiting technology was introduced into China in the late 1980 s and early 1990 s, especially during the period from 1990 to 1994, hundreds of production lines were introduced throughout the country, accounting for more than half of the world's manufacturers at that time. In the early stage of introduction, this anti-counterfeiting technology did play a certain role in anti-counterfeiting, but with the passage of time, laser holographic image production technology spread rapidly, and now it has been broken by counterfeiters from all aspects, almost completely losing the ability of anti-counterfeiting.

(II) Second Generation Improved Laser Holographic Image Anti-counterfeiting Technology

The proliferation of the first generation of laser holographic anti-counterfeiting technology has prompted people to seek to improve existing technologies. There are three main improved technologies: one is the application of computer image processing technology to improve the holographic image; the second is the transparent laser holographic image anti-counterfeiting technology; the third is the reflective laser holographic image anti-counterfeiting technology.

1. Application of computer image processing technology to improve holographic images

Computer image processing technology to improve laser holographic image has experienced two forms of development, the first form is computer synthetic holographic technology, this technology is a series of ordinary two-dimensional image after optical imaging, according to the principle of holographic image imaging after processing recorded in a holographic recording material, so as to form a computer pixel holographic image. When observing this pixel holographic image, you can see different three-dimensional images at different viewing angles, and its graphics and colors have extremely flexible dynamic effects, and are not limited by the direction of the reproduced light. The second form is computer-controlled direct exposure technology. Unlike ordinary holographic imaging, this technology does not require shooting objects, and the required graphics are completely generated by the computer. The computer controls two coherent beams to generate all patterns point by point in units of pixels. The included angle between the two beams can be changed at different points, thereby making a three-dimensional hologram with special effects.

2. Transparent laser holographic image anti-counterfeiting technology

Ordinary laser holographic images are generally made of aluminum-plated polyester film through molding (you can also use polyester film through molding and then aluminum plating). The effect of aluminum plating is to increase the intensity of reflected light to make the reproduced image brighter. The illumination light and the viewing direction are both on the side of the observer, and such a laser rainbow embossed hologram is opaque. The transparent laser holographic image is actually canceled the aluminized layer, and the holographic image is directly molded on the transparent polyester film. In 1996, the Ministry of Public Security of my country applied the transparent laser holographic image to the resident ID card. The ID card was covered with a transparent film. When the front of the ID card was observed under light, not only the content of the ID card could be seen clearly, but also the transparent film could be seen. The two-dimensional and three-dimensional rainbow holographic images (the Chinese and English characters of "Great Wall" and "China").

3. Anti-counterfeiting technology of reflective laser holographic image

The imaging principle of reflection laser holographic image is to shoot the incident laser on the transparent holographic latex medium, part of the light is used as the reference light, the other part passes through the medium to illuminate the object, and then the object is scattered back to the medium as the object light, the object light and the reference light interfere with each other, generating a multi-layer interference fringe surface inside the medium, after the medium negative is processed, a multi-layer translucent reflective surface is generated inside the medium (for example, there can be more than 20 reflective surfaces in a 6-micron thick latex layer). The hologram is irradiated with a white light point light source. The multi-layer translucent reflective surface generated inside the medium reflects the light back, and the virtual image of the original can be seen against the reflected light, thus it is called a reflective laser hologram.

(III) Third Generation Encrypted Holographic Image Anti-counterfeiting Technology

The encrypted hologram image refers to an encrypted image that is invisible or becomes some speckle by encrypting the anti-counterfeiting image using optical image encoding encryption techniques such as laser reading, optical miniaturization, low-frequency lithography, random interference fringes, moire fringes, etc.

1. Laser reading

The principle of optical conjugation is used to store text or image information in a holographic image. Under normal circumstances, this information will not appear. When irradiated with a laser pointer, people can see the stored information with the help of sulfuric acid paper or white paper. The stored information can be text, logo, grayscale image, or even an article, and there are two forms of expression: reflective and transmissive.

2. Optical miniature

The text information is recorded on the hologram in an optical miniature manner, which is usually difficult to identify with the naked eye. The specific content can only be observed under a 10-fold or even 100-fold magnifying glass. Under normal circumstances, the Chinese can be reduced to 0.1mm and the English can be reduced to 0.05mm.

3. Low frequency lithography

The pre-designed fringe pattern is directly recorded on the hologram in the form of miniature by non-interference. The fringe density of these patterns is 10 times lower than that of ordinary interference fringes, which is about 100 lines/mm. The intuitive effect is that some parts of the hologram have diffraction patterns similar to metallic luster. If the fringe pattern is a computer-generated hologram, the information can be reproduced by laser.

4. Random interference fringes

When making holograms, random mechanisms are introduced to record random interference patterns on holograms. This pattern has obvious characteristics and cannot be repeated. Even if the same person uses the same process at different times, the patterns produced are different. Therefore, it is a good anti-counterfeiting method. In addition to static plane interference fringes, the current has developed to dynamic, three-dimensional interference fringes, counterfeits simply can not copy.

5. Moore interference encryption

Using the Moire principle, that is, the principle that the stripes of two sets of periodic structures overlap can produce a third set of periodic structure patterns, in which one set of stripes changes its phase and encodes a pattern, which is usually hidden and cannot be distinguished. When overlapping with another set of periodic stripes, the pattern appears.

The encrypted holographic image has a certain anti-counterfeiting function because it is invisible or only shows a piece of noise light, if there is no key, it is difficult to decipher. But because it can not be distinguished in the usual environment, it does not have the ability to identify for the general public.

(IV) Fourth Generation Laser Holographic Anti-counterfeiting Technology

1. Combined hologram

A combined hologram is a hologram in which dozens or even hundreds of different two-dimensional images are recorded through dozens or even hundreds of exposures. The effect can be reflected from two aspects, one is similar to the plane dynamic design, can shoot a variety of patterns of the plane dynamic change pattern, the second is the use of 3D software or with the help of digital cameras, the three-dimensional target of each side and the change process over time recorded, the production of four-dimensional hologram, that is, the hologram can not only record and reproduce the object's three-dimensional space (X,Y,Z) characteristics, it can also record and reproduce the change of the three-dimensional object over time (T). This is a hologram with extremely high anti-counterfeiting performance. Compared with ordinary 2D/3D or true three-dimensional holograms, it has the following characteristics:

The amount of information is huge, the production process is complex: ordinary holographic anti-counterfeiting labels can often be completed through several exposures, and the production of four-dimensional holograms need to record dozens or even hundreds of frames of two-dimensional images, so that the number of exposures is ordinary holographic dozens or even hundreds of times, which requires special equipment and more sophisticated process to achieve.

②There are no restrictions on shooting images, which expands the application scope of laser holography, a high-tech means: ordinary holography records three-dimensional model requires 1:1 model entity to shoot, while four-dimensional holography first collects the information of objects from various angles, and then synthesizes the collected two-dimensional images to make holograms, thus there is no restriction on the shooting objects, which can be real people or real objects, even computer-constructed illusory objects. The ratio does not need to be 1:1.

③ True color four-dimensional display, ordinary holographic logo is far behind: traditional holographic logo can only achieve a sense of plane hierarchy, three-dimensional hologram can only show the three-dimensional characteristics of 1:1 still life, and can not restore the true color of the object. Four-dimensional holograms are different. While reacting three-dimensional space objects in true color, they can also attach the changes in the three-dimensional space over time. Such holographic logos are like a small TV with rich content. Designers can sprinkle on it.

2. True three-dimensional hologram

One of the important features of hologram is to realize three-dimensional display. True three-dimensional hologram is to use real three-dimensional carving model to make hologram. Its anti-counterfeiting significance lies in two aspects. First, the shooting difficulty of three-dimensional model hologram is much higher than that of ordinary 2D/3D, especially the combination of the two. Second, even if the counterfeits can make three-dimensional model hologram, the angle of three-dimensional carving and shooting will be very different, it's hard to succeed. Therefore, this is a high security hologram.