The principle of holography, in short, mainly uses the characteristics of pure laser color. In fact, the theory of holography was put forward by the British scientist Gabor as early as 1947. But it was not until the laser with high brightness, pure color and good coherence came out that holography was really photographed.
Holography and stereo photography are two different things. Although the stereoscopic color photo looks bright, layered and stereoscopic, it is still a one-sided image, and even the best stereo photo can't replace the real thing. For example, a square block of stereo photo, no matter how we change the observation angle, can only see the picture in the photo. But holograms are different. We can see the six sides of the square by changing the observation angle. Because holographic technology can record all the geometric features of objects on the negative, this is also the most important feature of holography.
The second feature of holography is that you can know the whole picture from 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 on 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 by a laser. The light waves reflected by small particles are basically spherical waves that are constantly expanding outward. We observe brighter particles. When shooting this small particle 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 particle. Photographic negatives can record the bright spot of this point, but they can't remember the position of small particles in three-dimensional space, and the printed photos have only one bright spot. There seems to be no three-dimensional sense. When shooting a hologram, a photographic lens is not needed, but a laser beam emitting plane waves and spherical waves reflected by small particles is irradiated on the photographic negative. The whole negative is illuminated, recording not a bright spot, but a group of concentric circles. When concentric circles are small, it looks like cutting a radish into pieces with a knife and piling them together to form a group of concentric circles. After the film is developed, it is put in its original position, and then irradiated at the shooting angle with a laser beam that emits plane waves. We can see that there is a bright spot in the original position where the tiny particles are located. 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 and this 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 made 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 the developed negative is irradiated with a reference beam, the light we see seems to come from the original. So 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 three-dimensional 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 have been studying and finally invented a holographic picture, which can also see the holographic scene under incandescent lamp. It is called white light holography or rainbow holography.
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 some small ideas. 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 per square millimeter. On this negative, a large photo of 3 10 square centimeter can be loaded per square millimeter. A small piece of 5 mm square film can hold 200 pages of books.
The main significance of the invention of holographic camera is not photography. As an aspect of laser technology, it 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, some people have made book inserts, trademarks and three-dimensional advertisements with holographic photos; Museums use it instead of displaying precious cultural relics. When a foreign machine tool manufacturing company went to another country to hold a product introduction meeting, 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 are more interesting to visitors.
A well-conceived hologram is also a beautiful work of art. The United States, France and other countries have holographic photo museums, which collect the most beautiful works in the world.
Holography can also record precious historical relics. In case the cultural relics are seriously damaged, even if nothing is left, we can still reconstruct them according to holography. For example, places of interest like Yuanmingyuan were burned down by Eight-Nation Alliance in those years. Although reconstruction is planned now, it is difficult to fully recover 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, what the audience sees is not on the screen, but among the audience, giving people a real feeling of being there. As for holographic TV, it is still under study because of its complex technical problems. 1982, the stereoscopic TV broadcast by German TV station is not laser holographic TV. Its principle is the same as that of ordinary three-dimensional movies, and a pair of special glasses should be worn when watching. It is predicted that by the end of this century, movies and television will be replaced again; 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. The concave lens can make the beam diverge, and the parallel beam becomes a spherical wave; The hologram shot with small particles mentioned above will also turn the parallel light reference beam into a spherical wave; Such a hologram is also a special concave lens. Optical elements such as convex lens and cylindrical lens can be made in a similar way. This assembly is as thin and light as paper and won't break. At present, telescopes made of holographic optical elements are almost as thick as ordinary myopia lenses. It is also reported that glass windows are made of holographic optical elements. This strange window glass will not affect people's sight, but it can reflect a lot of sunlight and act as a curtain; 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 test 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 let laser holography act as an "inspector" of the internal quality of finished products. When checking, add a little pressure or heat to the object being checked; If there are cracks and micropores on an object, its surface will change accordingly. Although the degree of this change is so subtle that the naked eye can't detect it at all, all these flaws and hidden dangers are exposed to the "golden eye" of holography. This method can not only accurately detect the internal quality, but also has the advantage of no damage to the detected object, and is especially suitable for the detection of valuables, such as precious cultural relics and ancient sculptures. Greek scientists used this method to find out the weathering degree of ancient statues. In production, this method is used to check the internal quality of precision parts, aircraft skin and aircraft tires. Laser holographic "inspector" has been used in foreign aircraft tire factories. This method is also used in biological research, such as studying the deformation of skull under stress, studying the growth rate of mushrooms and so on.
What is still developing is holographic storage technology. When we talk about the characteristics of holography, we mentioned the ability to store information, that is, the ability to record information. Theoretically, the information stored in optical disc is about 0/06 bit per square centimeter 108 bit per square centimeter, which is higher than 100 times! 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; In addition to scientific research, it can only be used as a high-grade work of art, and a new relief holographic technology appeared in the 1980s. To make holograms by this method, first of all, we must make metal micro-relief plates; Using it as a printing plate, the hologram is pressed out 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; In sunlight or light, it presents a variety of colors, which is more beautiful 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. You can't copy without the original. Therefore, it has become an effective means to prevent counterfeiting. Various holographic signs have appeared on banknotes, credit cards, magnetic cards and diplomatic visas to prevent counterfeiting. In China, many manufacturers use holographic trademarks to prevent people from forging trademarks and deceiving 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. Inventor Garber studied this subject in order to improve the resolution of electron microscope. He designed this new imaging method and published it in 1948 Science Journal. But there was no such good monochromatic light as laser at that time, and there were some technical difficulties. Garber didn't get any results, and no one paid attention to his paper.
It was not until 1964 more than ten years later that holographic technology began to develop because of the appearance of the ideal light source-laser. Soon, holography has become a new technology with wide application and unlimited development potential. Garber won the Nobel Prize in Physics in 197 1 year for his pioneering holographic theory. He himself is recognized as the "father of holography" by the world.