Development of holographic anti-counterfeiting

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

(1) The first generation holographic anti-counterfeiting technology is laser molded holographic image anti-counterfeiting.

Holography was discovered by American scientist MJ Buerger when he photographed the atomic structure of crystal with X-rays, and together with dennis D Gaber, he established the holographic theory: based on the principle of double-beam interference, the object light and another beam (reference beam) which is coherent with the object light can produce interference patterns, so that the phases can be "merged", so that the lower phase and amplitude can be recorded simultaneously with the photosensitive film, and the holographic image can be obtained. However, holography is based on the principle of interference and must be recorded with high-density (resolution) photographic film. Due to the poor monochromaticity and coherence of ordinary light sources, the development of holographic technology is slow, and it is difficult to shoot decent holograms. It was not until the appearance of laser in the early 1960s that its characteristics of high brightness, high monochromaticity and high coherence quickly promoted the development of holographic technology. A variety of holograms have been produced, and the holographic theory has been well verified. However, due to the special requirements of shooting and reproduction, it has been almost confined to the laboratory since its birth.

At the end of 1970s, it was found that holographic pictures had a surface structure including three-dimensional information (that is, criss-crossing interference fringes), which could be transferred to high-density photographic negatives and other materials. 1980, American scientists transferred the holographic surface structure to polyester film by using relief holographic technology, thus successfully printing the world's first relief holographic picture. This kind of laser holographic picture, also called rainbow holographic picture, is made on plastic film by laser plate making, which produces colorful diffraction effect and makes the picture have two-dimensional and three-dimensional sense of space. Under ordinary light, hidden images and information will reappear. When light shines from a certain angle, a new image will appear. This kind of relief holographic picture can be copied in large quantities as quickly as printing, with low cost, and can be used in combination with various printed matter. At this point, holography has taken a decisive step towards social application.

At that time, the production technology of this molded holographic picture was very advanced, and only a few people mastered it, so it was used as an anti-counterfeiting mark. Its anti-counterfeiting principle is:

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

2. The holographic information of this holographic image can't be captured by ordinary photography, so it is difficult to copy the holographic pattern.

JohnnyWalkeWhishy (a whisky) first used holographic pictures as anti-counterfeiting marks. When it was applied in Thailand, it was said that the sales volume increased by about 45%.

Laser-molded holographic anti-counterfeiting technology was introduced to China in the late 1980s and early 1990s, 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. At the initial stage of introduction, this anti-counterfeiting technology did play a certain anti-counterfeiting role, 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 its anti-counterfeiting ability.

(2) The second generation of improved laser holographic image anti-counterfeiting technology.

With the popularization of the first generation of laser holographic anti-counterfeiting technology, people have to start to seek the improvement of the existing technology. There are three kinds of improvement techniques: one is to improve holographic images by using computer image processing technology; The second is the anti-counterfeiting technology of transparent laser holographic image; The third is the anti-counterfeiting technology of reflective laser holographic image.

1. Using computer image processing technology to improve holographic images.

The improvement of laser holographic image by computer image processing technology has gone through two development forms. The first form is computer synthetic holography, which records a series of ordinary two-dimensional images on a holographic recording material after optical imaging according to the imaging principle of holographic images, thus forming a computer pixel holographic image. When observing this kind of pixel holographic image, different three-dimensional images can be seen from different perspectives, and their graphics and colors have extremely flexible and dynamic effects, and are not limited by the direction of reproduced light. The second form is computer-controlled direct exposure technology, which is different from ordinary holographic imaging. This technology does not need to shoot objects, and the required patterns are completely generated by computers. By computer controlling two coherent beams to generate all patterns point by point, the angle between the two beams can be changed for different points, thus making a three-dimensional hologram with special effects.

2. Transparent laser holographic image anti-counterfeiting technology.

Ordinary laser holographic images are generally molded with aluminized polyester film (or molded with polyester film first and then aluminized). The function of aluminum plating is to increase the intensity of reflected light and make the copied image brighter. The illumination light and observation direction are on the observer side, so the laser rainbow relief hologram is opaque. In fact, the transparent laser holographic image is to cancel the aluminum plating layer and directly mold the holographic image on the transparent polyester film. 1996 The Ministry of Public Security of China applies transparent laser holographic images to resident identity cards and covers them with transparent films. When you look at the front of the ID card under the light, you can not only see the contents of the ID card clearly, but also see the two-dimensional and three-dimensional rainbow holographic images (the words "Great Wall" and "China" in Chinese and English) appearing on the transparent film.

3. Reflective laser holographic image anti-counterfeiting technology.

The imaging principle of reflective laser holographic image is that incident laser is irradiated on a transparent holographic latex medium, some light is used as reference light, and the other light is used to irradiate an object through the medium, and then the object is scattered back to the medium as object light, and the object light and the reference light interfere with each other, resulting in multi-layer interference fringe surfaces inside the medium, and the negative film of the medium is processed to produce multi-layer semi-transparent reflective surfaces inside the medium (for example, there can be more than 20 reflective surfaces in a 6 micron thick latex layer). When the hologram is illuminated by a white light source, the multi-layer semi-transparent reflecting surface generated in the medium reflects the light back, and the virtual image of the original object can be seen against the reflected light, so it is called a reflective laser hologram.

(3) The third generation encryption holographic image anti-counterfeiting technology.

Encrypted holographic image refers to an invisible or speckled encrypted image obtained by encrypting an anti-counterfeiting image by using optical image coding and encryption technologies such as laser reading, optical miniaturization, low-frequency lithography, random interference fringes and moire fringes.

1. Laser reading

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

2. Optical miniaturization

It is usually difficult for the naked eye to recognize the text information recorded on the hologram in an optical miniature way, and the specific content can only be observed under a magnifying glass of 10 times or even 100 times. In general, Chinese can be reduced to 0. 1mm, and English can be reduced to 0.05 mm

3. Low frequency lithography

The pre-designed fringe pattern is recorded directly on the micro hologram in a non-interference way. The fringe density of these patterns is about 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 appear diffraction patterns similar to metallic luster. If the fringe pattern is a computer-generated hologram, the information can be copied by laser.

4. Random interference fringes

When making holograms, random mechanism is introduced to record random interference patterns. This model has obvious characteristics and cannot be repeated. Even if the same person uses the same technology, the patterns produced at different times are different, which is a good anti-counterfeiting method. In addition to static plane interference fringes, it has developed into dynamic and three-dimensional interference fringes, and counterfeiters can't copy them at all.

5. Moire interference encryption

Based on Moore's principle, that is, the overlapping of two groups of periodic structure stripes can produce a third group of periodic structure patterns. The phase of one group of stripes is changed and encoded into a pattern, which is usually hidden and indistinguishable. When it overlaps with another group of periodic stripes, the pattern appears.

Because the encrypted holographic image is invisible or only shows a piece of noise, it is difficult to decipher without a key, and it has certain anti-counterfeiting function. But because it can't be distinguished in ordinary environment, it doesn't have the ability to be recognized by the general public.

(D) the fourth generation of laser holographic anti-counterfeiting technology

1. combined hologram

Combination hologram is a hologram recorded by exposing dozens or even hundreds of different two-dimensional images for dozens or even hundreds of times. Its effect can be reflected in two aspects: first, it is similar to plane dynamic design, which can shoot all kinds of plane dynamic changing patterns; The other is to use 2D/3D software or digital camera to record the faces of three-dimensional objects and their changes with time to make four-dimensional holograms, that is, holograms can not only record and reproduce the three-dimensional space (x, y, z) characteristics of objects, but also record and reproduce the changes of three-dimensional objects with time (t).

① The amount of information is huge and the manufacturing process is complicated: ordinary holographic anti-counterfeiting labels often need multiple exposures to complete, while the production of four-dimensional holograms needs to record dozens or even hundreds of two-dimensional images, so the exposure times are dozens or even hundreds of times that of ordinary holograms, requiring special equipment and more precise technological processes.

② There is no restriction on the shooting of images, which expands the application scope of laser holography as a high-tech means: ordinary holography uses 1: 1 model to record three-dimensional models, while four-dimensional holography first collects information from all angles of objects, and then synthesizes the collected two-dimensional images to make holograms, so there is no restriction on the shooting objects, which can be real people, physical objects or even imaginary objects built by computers. The ratio does not have to be 1: 1.

③ Four-dimensional display of true color is far behind ordinary holographic signs: traditional holographic signs can only achieve plane layering, while three-dimensional holograms can only display the three-dimensional characteristics of 1: 1 still life, and cannot restore the true color of objects. On the other hand, four-dimensional holography reflects three-dimensional objects with real colors, but it also carries the changes of three-dimensional space with time. Such a holographic logo is like a small TV with rich content, which designers can enjoy to their heart's content.

2. True 3D hologram

An important feature of holograms is that they can be displayed in three dimensions. True three-dimensional holograms are made of true three-dimensional sculpture models. Its anti-counterfeiting significance lies in two aspects. Firstly, the shooting difficulty of 3D model hologram is much higher than that of ordinary 2D/3D, especially the combination of the two. Second, even if the counterfeiter can make a three-dimensional model hologram, the angle of the object will be very different between three-dimensional carving and shooting, and it is difficult to succeed. Therefore, it is a hologram with high security.