The principle of holography, in short, mainly uses the pure color characteristics of laser. In fact, the theory of holography was put forward by British scientist Gabriel as early as 1947. But it was not until the laser with high brightness, pure color and good coherence appeared that holography was really photographed.
Holography and stereo photography are two different things. Although stereoscopic color photos look bright, layered and stereoscopic, they are still single-sided images, and even the best stereo photo can't replace the real thing. For example, no matter how we change the observation angle of a square block, we can only see the picture in the photo. But holograms are different. We can see this square by changing the observation angle.
The second feature of holography is that we can know the whole picture at one point. When the hologram is damaged, even if most of it is damaged, we can still see the whole picture of the original object in this hologram from the remaining half. This is not good for ordinary photos, even if a corner is lost, you can't see the picture of that corner.
The third feature of holographic photos is that multiple holographic photos can be recorded in layers on a holographic negative without interfering with each other when displaying pictures. It is this layered recording that enables holograms to store a large amount of information.
Why do holograms have such characteristics? Why don't ordinary photos have these characteristics? This should start with the shooting principle.
If a tiny particle is irradiated with a laser beam, the light wave reflected by the tiny particle is basically a spherical wave extending outward. When we look at this small grain, it is a bright spot. When shooting small particles with a camera, light waves form a bright spot on the negative through the lens, and the brightness of this bright spot is related to the light intensity reflected by the small particles. Photographic negatives can record this bright spot, but we can't remember the position of this small particle in three-dimensional space. There is only one bright spot in the printed photo. There seems to be no three-dimensional sense. When taking a hologram, a laser beam emitting plane wave and spherical wave reflected by small particles shines on the photographic negative together. The whole negative is illuminated, recording not a bright spot, but a group of concentric circles. When concentric circles are small, they look like a radish cut into pieces with a knife and piled together. Become a set of concentric rings. After the film is washed, put it back in its original position, and then use a laser beam that emits plane waves when shooting to shine on the film at the angle when shooting. We can see a bright spot where the tiny particles used to be. Attention! This bright spot is in space, not on the film, and the light we see seems to come from this bright spot. So the hologram records not only a bright spot, but also the spatial position of the bright spot, or the whole light wave emitted by the bright spot. The whole mystery lies in this novel shooting method, which is a parallel (plane wave) laser beam. This laser beam is called a reference beam.
So any object can actually be regarded as a three-dimensional image composed of countless bright spots with different shades. The hologram shot by the above shooting method is a complex figure composed of countless concentric circles, which also looks gloomy. Similarly, this hologram not only records the brightness of each point of the object, but also records the spatial position of each point. When a developed negative is irradiated with a reference beam, the light we see seems to be emitted from the original object. Therefore, we say that it records all the light information emitted by the object, hence the name hologram. However, only under the irradiation of laser can the eyes have stereoscopic images, and laser is an expensive device. It is impossible to equip a photo with a laser, except in scientific research departments and special places. In view of this shortcoming, scientists continued to study and finally invented an incandescent lamp.
The negative of laser holography can be special glass, latex, crystal or thermoplastic. A small special glass can store all the contents of millions of books in a large library.
If you pay attention to the photos in the newspaper, you will find that they are made up of dots. Each point is called a pixel, and its density is about several points per square millimeter. The special glass film for holography is about 10 micron thick, and the density of image points is more than 2000 points/mm2. On this negative, 365,438+pictures can be loaded per square millimeter.
The invention of holographic camera, as an aspect of laser technology, has a wide range of practical value in industry, agriculture, scientific research and other fields.
In photography, this is a brand-new technology. Because hologram has a realistic stereoscopic effect, it has a unique effect of replacing ordinary photos. In foreign countries, holographic photos have been made into book inserts, trademarks and three-dimensional advertisements. Museums use it to replace precious cultural relics. When a foreign machine tool manufacturing company held a product introduction meeting in another country, it held a machine tool exhibition with holograms instead of objects. The exhibition hall is covered with holograms of various machine tools. These holograms look no different from real machine tools, but they attract more visitors' interest.
Ingenious holograms are also exquisite works of art. The United States, France and other countries have holographic museums, which collect the most exquisite works in the world.
Holography can also record precious historical relics. In case of serious damage to cultural relics, even if they are gone, we can still rebuild them according to holographic technology. For example, a scenic spot like the Yuanmingyuan in Beijing was burnt down by Eight-Nation Alliance in those years, but now it is difficult to fully recover it because we don't know the whole picture. If holography was invented 100 years ago, things would be simple.
Inspired by holographic photos of three-dimensional scenes, scientists thought of holographic movies and holographic television. Experimental holographic stereoscopic films have appeared in the former Soviet Union. When this kind of film is shown, the scene seen by the audience is not on the screen, but among the audience, which makes people feel immersive. As for holographic TV, it is still under study because of the complicated technical problems involved. 1982, a stereoscopic TV broadcast by German TV station, is not a laser holographic TV. Its principle is the same as that of ordinary three-dimensional movies. Wear a special pair of glasses when watching. It is predicted that by the end of this century, movies and television will be replaced. At that time, people's cultural and entertainment life may become more colorful because of the emergence of laser panoramic stereo movies and laser stereo TV.
Another important application of holography is to make holographic optical elements, which can replace glass in some special occasions. This special optical element has the advantages of convenient processing, small volume, light weight and thinness. A concave lens can make a beam diverge, and a parallel light wave will become a spherical wave. The hologram shot with small particles mentioned above will also turn the parallel light reference beam into a spherical wave; This hologram is a special concave lens. Optical elements such as convex lenses and cylindrical lenses can be manufactured in a similar way. Such components are as thin as paper and will not break. At present, telescopes made of holographic optical elements are almost as thick as ordinary myopia lenses. It is also reported that the glass window made of holographic optical elements will not affect people's sight, but it can reflect a lot of sunlight and has the function of curtains. More interestingly, it can concentrate the sunlight reflected by itself on a row of solar cells installed under the window eaves and convert it into electric energy for indoor use, killing two birds with one stone.
Holographic technology has the ability to see through everything. Because the hologram can accurately reproduce the original, we can use it as a standard to check whether the original has changed. In fact, as long as there is a change in 1 micron, it can be detected by holographic technology. Scientific research and production departments also use laser holography as a teasing inspector for the internal quality of finished products. When checking, add a little pressure or heat to the inspected object; If there are cracks and micropores in an object, its surface will change accordingly. Although the degree of this change is extremely subtle and imperceptible to the naked eye, all these flaws and hidden dangers are exposed under fascinating holography. This method can not only accurately check the internal quality, but also has the advantage of no damage to the inspected object, especially for valuables. For example, the detection of precious cultural relics and ancient sculptures. Greek scientists used this method to find out the weathering degree of ancient statues. In production, they use this method to check the internal quality of precision parts, aircraft skins and aircraft tires. In foreign aircraft tire factories, laser holography has been used to tease inspectors. This method is also used in biological research, such as studying the deformation of skull under pressure and studying the growth rate of mushrooms.
What is still developing is holographic storage technology. We talked about the characteristics of holography, that is, the ability to store information. Theoretically, if information is stored on an optical disc, about 106 bits can be stored per square centimeter, while if information is stored on a hologram, 108 bits can be stored per square centimeter, which is 0/00 times higher than/kloc-0! And the time to read information is only one millionth of a second!
Now, information can be stored in materials. The material used in holography is not a thin film, but a whole crystal that can store 65438+ ten thousand books. A library only needs to store a small number of recording crystals. It seems a bit whimsical, but it is hopeful. More importantly, the development of holographic storage will promote the development and upgrading of computers.
Generally, holograms can only be made one by one, and the price is very high; Apart from scientific research, it can only be regarded as a high-grade work of art, and a new relief holographic technology appeared in the 1980 s. To make a hologram by this method, a metal micro-relief plate must be made first. Using it as a printing plate, holograms can be printed on special paper coated with metal film. This is more convenient than printing stamps, and can be produced in large quantities, with greatly reduced cost and wider application.
This kind of holography not only has three-dimensional effect; It presents a variety of colors in sunlight or light, and looks more gorgeous on a silvery white metal background. People use it to decorate books, toys and souvenirs, which is very attractive.
This kind of holography also contains a wealth of information, and it depends entirely on the set and shooting method used in the production, just like adding a password. Without the original printing plate, you can't copy it. Therefore, it has become an effective means to prevent counterfeiting. Various holographic signs have appeared on banknotes, magnetic cards and diplomatic visas to prevent counterfeiting. In China, many manufacturers have also adopted holographic trademarks to prevent people from forging trademarks to deceive customers.
It is worth mentioning that holographic photography, a major technological achievement, was invented in a scientific research field that has nothing to do with ordinary photography. The inventor Garber studied this subject in order to improve the resolution of electron microscope. He designed this new imaging method and published it in the scientific journal 1948. But there was no such good monochromatic light as laser at that time, and there were some technical difficulties. Garber didn't get results. His thesis
It was not until 1964 more than ten years later that holographic technology began to develop. Soon, holography has become a new technology with wide applications and unlimited development potential. Garber won the 197 1 Nobel Prize in physics for his pioneering theory of holography, and was recognized as the father of holography in the world.