(l) Laser Communication
Transmission of information by light is very common today. For example, ships communicate in the language of lights, and traffic lights are dispatched in red, yellow and green. But all these ways of transmitting information with ordinary light can only be limited to short distances. If you want to transmit information directly to a distant place through light, you can not use ordinary light, but only move the laser.
So how do you transmit a laser? We know that electricity can be transported along copper wires, but light cannot be transported along ordinary metal wires. For this reason, scientists have developed a thin wire that can transmit light, called an optical fiber, or fiber optics for short. Optical fibers are made of a special glass material, thinner than a human hair, usually 50 to 150 microns in diameter, and very soft.
In fact, the inner core of the fiber is a high refractive index of transparent optical glass, while the outer cladding is made of low refractive index glass or plastic. Such a structure, on the one hand, can make the light refracted along the inner core forward, just like water in the tap water pipe flow forward, electricity in the wire forward transmission, even if a thousand times around a hundred fold has no effect. On the other hand, the low-refractive-index cladding prevents light from escaping, just as water pipes don't seep, and the insulation of electrical wires doesn't conduct electricity.
The emergence of optical fibers solves the problem of transmitting light, but it doesn't mean that with it any light can be transmitted far, far away. Only high brightness, pure color, good directionality of the laser, is the most ideal light source for transmitting information, which is input from one end of the fiber, with little loss and output from the other end. Therefore, optical communication is essentially laser communication, which has the advantages of large capacity, high quality, wide source of materials, strong confidentiality, durability, etc. It has been hailed by scientists as a revolution in the field of communication, and is one of the most brilliant achievements in the technological revolution.
Where is laser communication advanced? The advantages of laser communication are first of all the large capacity. How much capacity does it have? When we usually talk on the phone, talking sometimes strings in disjointed speech. This fighting phenomenon is due to a pair of telephone lines can only pass through a phone, if another string into a phone, the normal call will be interfered with both sides. If there are 10 pairs of people talking at the same time with a pair of telephone lines, it is equal to 20 people talking at the same time, it is simply impossible to talk. In order to solve this problem, it is necessary to use the carrier wave and other methods, so that each road phone in each band. As the ordinary telephone frequency range of 300 to 400 Hz, and in a pair of telephone lines on the highest frequency of only 1500 kHz, so in a pair of telephone lines can only be passed at the same time more than a dozen ways to telephone. Obviously, such telecommunication capacity is far from meeting the requirements of today's information society.
If we compare the amount of information transmitted by an ordinary telephone to that of a trolley, then laser communication is a car. Since the frequency of laser is much higher than that of radio waves, the information capacity of laser communication is one billion times larger than that of electrical communication. A single optical fiber, which is thinner than a strand of hair, can transmit tens of thousands of telephone calls or thousands of television programs. A fiber-optic cable made up of 20 fibers is only as thick as a pencil and can make 76,200 calls per day. By contrast, a cable made up of 1,800 copper wires, about 7.6 centimeters in diameter, can make only 900 calls a day.
Particularly surprising is the fact that fiber-optic communications are particularly well suited to the transmission of television, images and numbers. A pair of optical fibers can reportedly deliver a full set of the Encyclopedia Britannica in less than a minute.
In addition, the material used to make optical fibers is quartz, a sand found everywhere on Earth, and it only takes a few grams of quartz to make a 1-kilometer-long fiber. In this way, not only is the raw material inexhaustible, inexhaustible, but also can greatly save copper and aluminum. Because of this, the world's developed countries are now competing to study laser communications. So laser communication has become the favorite of the competition for development.
In the history of communications technology, the rapid development of fiber optic communications technology is unprecedented. Take a few milestones in the history of communications technology, the telephone from invention to application, it took about 60 years, and telephone communication is still a large number of common use. Radio technology (e.g., the telegraph) also took about 30 years from invention to application. Television technology, while developing more rapidly, was still gestating for about 14 years. Laser communication, on the other hand, from the birth of the first low-loss optical fiber to its application, the total *** only 5 years. Now laser communication is not only widely used, but also formed a huge fiber market.
In May 1977, the United States has a large company called Telegraph and Telephone Company, which is in the city of Chicago between the two telephone offices, laid the world's first short-distance optical fiber communication lines, and since then in the whole of the United States in nearly a hundred places to establish a total of several hundred kilometers of short-distance laser communication lines. This means that in the short distance, laser communication has begun to replace ordinary electrical communication. By 1983, the 600-kilometer-long fiber-optic communication between New York and Boston in the United States had been put into use.
Following the United States behind is Japan. 1984, Japan completed from Hokkaido's Sapporo to Fukuoka, Kyushu, long-distance fiber-optic communications trunk line, the total length of 2,800 kilometers, the middle of the link with more than 30 cities. 1993 December, China and Japan across the East China Sea fiber-optic cables have been laid successfully. A 10,000-kilometer-long undersea fiber-optic cable across the Pacific Ocean between Japan and the United States is also being designed.
Because of the booming development of optical fiber communications, the United States, Japan, Britain, France and other industrially developed countries have set up optical fiber, optical fiber cable production enterprises. The world's three famous fiber optic cable company - the United States of America's Western Electric Company, Corning Incorporated and Japan's Sumitomo Corporation, optical fiber production is more than 120,000 kilometers per year.
In short, industrially developed countries have established a national fiber-optic communication network in order to completely replace the current copper wires and cables, this vast technical project is estimated to be completed by the year 2000. By that time, laser communication will bring great changes to our planet. For example, without leaving home, you can use the fiber optic network at home to deal with documents or to participate in a meeting; or home fiber optic network connected to the shopping center, as in the supermarket, sitting at home to buy the goods you need, the payment must be settled only with the electronic financial shopping system. Medical centers around the world can also view the patient's condition and laboratory reports from the screen, and accordingly issued a prescription order, so as to truly achieve the "showman does not go out, you can know the world", "planning in a tent, the victory in a thousand miles away.
Lasers and optical fibers can also transmit images. First of all, the diameter of the single optical fiber than the human hair is thin enough to group into fiber bundles. In the process of transmitting information, there are two types of fiber bundles commonly used: one is called a light-transmitting bundle and the other is called an image-transmitting bundle. The task of the beam is to transmit light from one end to the other. The structure of the transmission beam is relatively simple, it is made of a number of monofilaments glued together, and then its end face polishing, grinding, in order to reduce the light into the optical fiber when the reflection and scattering losses, and then in the transmission beam outside the plastic sheath.
Because an optical fiber can only transmit a point of light, to transmit the entire image must be optical fiber one by one neatly arranged, so that the composition of the optical fiber bundle is called the transmission beam.
In the image beam, all the optical fibers are neatly arranged, the two ends of the position are strictly corresponding to one by one, there is no confusion, like a neat chopsticks. For example, one end of an optical fiber is in the eighth row and eighth column of the beam, and the other end of the fiber is also in the eighth row and eighth column of the beam.
The beam transmits the image, first splitting the image into a mesh, i.e., an image is broken down by countless optical fibers into countless pixels, and then transmitted. One fiber is responsible for transmitting one image element, and countless fibers will be able to transmit the entire image to the other end. If you want to make the image transmitted clearly, we must choose as much as possible, the diameter of the thin fiber, because the finer the fiber, in a certain image beam can accommodate into more light beams, so that it can transmit more like elements. Obviously, the more pixels, the clearer the image.
The beams used today are made up of tens of thousands of optical fibers, and it's not easy to align them neatly. Arranged, and then an organic adhesive called epoxy resin will be glued to the ends, so that the fiber bonding fixed, to ensure that the two ends of the fiber one to one. The two end surfaces should also be smoothed and polished. As for the middle part does not have to be glued, but as loose as the strings of the erhu, only to be added to the outside of the protection of the plastic sleeve, so that the transmission beam is both soft, but also can be bent arbitrarily.
In addition to transmitting images, the beam can also transmit general symbols or numbers, as well as zoom in and out of the image.
To enlarge an image, the beam can be made large at one end and small at the other, like a cone. When an image element is passed from the small end to the large end, the entire image is enlarged. Conversely, if the image is sent from the large end to the small end, the entire image is reduced.
In addition, images can be altered using optical fibers. If you need to intentionally disrupt the arrangement of optical fibers, you can make the exit end of the image element does not fall on the original corresponding point, but falls on the subjective conception of the point, so the image is changed. If the fiber at the inlet end of the image element is made square and the fiber at the outlet end is made circular, the square image element can be turned into a circular image element.
In short, the fiber optic image beam has great potential for development, in the future of optical information processing technology will increasingly show its unique role.
(2) Material Processing
Drilling, cutting, welding, and quenching are the most common operations used in processing metal materials. Since the introduction of lasers, a whole new situation has opened up in terms of the strength, quality and scope of processing. In addition to metallic materials, lasers are capable of processing many non-metallic materials.
Laser Drilling MachineBefore the introduction of the laser drilling machine, the drilling of various mechanical parts relied on electric drilling machines or punching machines. But mechanical drilling is not only inefficient, and drilled holes in the surface is not clean enough.
The principle of laser drilling, is the use of laser beam aggregation to make the focus of the metal surface temperature rises rapidly, the temperature rise up to l00 million degrees per second. When the heat is not yet dispersed before the beam fuses the metal until it vaporizes, leaving a small hole. Laser drilling is not limited by the hardness and brittleness of the material being processed, and it is exceptionally fast, so fast that small holes can be drilled in thousands of seconds, or even millions of seconds.
For example, if you need to drill hundreds of microscopic holes in sheet metal that are difficult to detect even with the human eye, it is obvious that an electric drill is not up to the task, but a laser drill can do it all in 1 to 2 seconds. If you use a magnifying glass to these micro-holes for a closer look, then you can find the micro-hole surface is very neat and clean.
Laser drilling can also be used to process watch diamonds. It can drill 20 to 30 holes per second, hundreds of times more efficient than mechanical processing, and high quality. At the same time, laser drilling, like laser cutting, which we'll talk about below, is a non-contact process, i.e., it doesn't rely on a steel drill bit to gradually drill through the metal material, as is the case with machining. As a result, laser operations can function in automated continuous processing, or in special environments with ultra-clean, vacuum conditions.
Laser cutting machine know the principle of laser drilling, it is easy to understand why the laser can cut metal materials: as long as you move the workpiece or move the laser beam, so that the drilled holes connected to the edge of the line, it will naturally be able to cut down the material. And, no matter what kind of material, such as steel, titanium plate, ceramics, quartz, rubber, plastics, leather, chemical fiber, wood, etc., the laser is like a handle of iron as mud, cutting wood as dust of the lightsaber, and, cutting edge is very clean.
Laser welding machine laser can be used to weld because of its high power density. The so-called high power density means that it can concentrate a very high amount of energy per square centimeter of area. How high is the power density of the laser? We can make a comparison: the factory is usually used for welding acetylene flame can be two pieces of steel plate welded together, the power density of this flame can reach 1,000 watts per square centimeter; argon arc welding equipment power density is also high, can reach 10,000 watts per square centimeter. But these two welding flame can not be compared with the laser, because the power density of the laser is ten million times higher than them. Such high power density can not only weld the general metal materials, but also can weld hard and brittle ceramics.
Laser quenchingTraditional quenching methods are very simple, the first blade red, and then suddenly immersed in cold water, after this hot and cold treatment, the hardness of the blade is greatly improved. However, this quenching is obviously not very convenient, the effect is not necessarily ideal.
Laser quenching, is a laser scanning tool or parts need to be quenched on the part, so that the temperature of the scanned area increases, while not being scanned to the part is still maintained at room temperature. Due to the fast heat dissipation of the metal, the laser beam just swept, this part of the temperature drops sharply. The faster the temperature drops, the higher the hardness. If the scanned area is then sprayed with a fast coolant, the hardness can be far more desirable than normal hardening.
(3) laser phototypesetting
Phototypesetting is actually the introduction of the principle of optical photography. Typesetting with movable type, must be based on the manuscript, according to the sample check out a variety of sizes, fonts and symbols for different typesetting. Photographic typesetting is much easier, it is through the typesetting machine on the lens, to change the size and shape of the characters. As for why the lens can change the size and shape of the characters, which is actually the same as we look at the "ha-ha mirror".
When using photographic typesetting, simply pass the light source through the lens to the required text and symbols, in the light-sensitive photographic paper imaging, and then after the development and fixation of the formation of a photographic negative. Then, just print it like a photo.
Photographic typesetting can use two kinds of light source, just said is an ordinary light source, compared with the laser typesetting time-saving and labor-saving. Because of the high brightness of the laser, light color, can greatly improve the clarity of the image, printed book quality is naturally high. How does it work? First of all, through the computer to turn the text into a point, and then use the point to control the laser scanning photographic negative, before the real shot holographic photo.
Holograms and stereoscopic photos are two different things. Although three-dimensional color photographs look colorful, layered, rich in three-dimensional sense, but it is still a one-sided image, and then the best three-dimensional photo can not replace the real thing. For example, a square wooden block of three-dimensional photo, no matter how we change the observation angle, can only see the picture on the photo, but the holographic photo is different, as long as we change the angle of observation, you can see the six aspects of the square. Because holographic technology can record all the geometric feature information of the object on the negative, which is one of the most important features of holographic photography.
The second important feature of holograms is the ability to see the whole picture in one spot. When the hologram is damaged, even if it is half damaged, we can still see the full picture of the original object on this hologram from the remaining half. This doesn't work for a normal photo, even if one corner is lost, the image on that corner is not visible.
The third feature of holograms is that multiple holograms can be recorded on a single holographic negative in layers, and they do not interfere with each other when they are displayed. It is this layered recording that allows holograms to store huge amounts of information. Laser holograms can be based on special glass, latex, crystals or thermoplastics. A small piece of special glass, can be a large library of millions of books all stored in the content. Holograms are becoming increasingly versatile.
Holograms can record valuable historical artifacts, and in the event that a monument is severely damaged, we can still rebuild it based on the hologram, even if there is nothing left. For example, like the Yuanmingyuan in Beijing, a famous place, was burned by the Eight-Power Allied Forces, although now intends to rebuild, because I do not know the original appearance of the whole, it will be difficult to fully recover. If holograms were invented 100 years earlier, things would be better.
Holograms can also be used in industry as non-destructive testing. What is non-destructive testing? It means that laser holography can be used to check products for tiny defects without damaging them at all.
What's more interesting is that holographic photography is also being used to shoot holographic movies and television, and soon viewers will be able to see real-life images. This means that a laser "hits" the light-sensitive paint on the negative, leaving countless corresponding dots, which are developed and fixed to become text or images again. Here, the laser beam is equivalent to an electron beam, photographic film is equivalent to a TV screen. Next, with the negative containing text and images can go to print books and magazines. The reason why color TV sets can display red, green, blue, is because the screen is coated with three-color phosphor, they will show three colors under the impact of electrons. And laser phototypesetting can also use a similar principle, printing a beautiful color picture to.
(4) laser applications in medicine
Laser applications in the field of medical equipment is a lot of results, it can play the role of drills, scalpels, welding torches and many other roles.
Welding torches and drills in ophthalmology, lasers are mainly used to treat retinal detachment. Retinal detachment is a tricky condition in which a patient's retina becomes detached from the inner wall of the eye and is unable to produce vision. Before lasers were available, patients feared that blindness would be unavoidable.
Now, doctors can point a laser at the bottom of the patient's eye, which emits a beam of laser light and heats the retina to bring it back together with the inner wall of the eye. The whole process takes less than a few minutes, and the laser beam acts like a welding torch, welding the patient's retina in place.
In addition to welding, the laser torch can also be used for cutting.
Cataracts are common among the elderly. The patient's lens, a convex lens at the front of the eye, gradually becomes cloudy and inelastic from its original transparent elastomer, so light cannot pass through the lens and fall onto the retina at the bottom of the eye, and the patient gradually loses sight of things. The traditional treatment for cataracts is to cut a slit in the front of the eye and insert a thin metal needle through the slit. This metal needle is so cold that it freezes the cloudy lens and sticks to the needle, which is then brought out together through the small opening, making the whole procedure more cumbersome, obviously.
If the treatment is done with a medical laser, it is not only convenient, but also effective. The chaotic membrane on the surface of the lens can be quickly removed by simply aiming the laser beam at the anterior or posterior surface of the lens inside the eye.
In dentistry, lasers can replace dental drills. According to the World Health Organization, the incidence of dental caries in children is quite high, reaching about 75%. With laser treatment of teeth, the patient has almost no discomfort, and as long as there is no inflammation, the problem can be solved in one treatment. The dental laser is the little brother of the laser, it has a very small power of only 3 watts, equivalent to an energy saving lamp, and produces almost no heat. Its emitting end is actually a light-guide fiber as thin as a strand of hair.
When treating a carious lesion, you only need to bring the fiber's emitting end close to the carious lesion, send out a laser beam, and the carious tissue will decompose and then be rinsed away with water. If the caries is only superficial damage to the tooth enamel, the laser beam will seal the tiny holes in the damaged area one by one, thus preventing the lactic acid from corroding the dentin. If carious holes have already appeared, after drilling and cleaning with the laser beam, the artificial enamel material can be filled into the cavity, and then the joint can be heated with the laser, so that the artificial enamel material can be fused with the tooth enamel. Laser dental treatment is not only painless and rapid, but also has a good effect after treatment.
Laser scalpel if you want to use a laser knife to the patient's bladder, heart, liver, stomach, intestines and other important internal organs surgery, the difficulty. How can a laser get into a person's internal organs? This depends on a treasure in the hands of the doctor, this treasure is the laser fiber endoscope.
The so-called endoscope is an optical device that doctors use to insert into the human body to directly observe the organs. However, the usual endoscope is relatively large and rough, and can only be inserted from the patient's mouth along the esophagus to the stomach to observe. Stomach insertion is very difficult and painful for the patient. Laser fiberoptic endoscopes are completely different. Endoscopes made of optical fibers are soft, thin, and bendable, and when it is inserted into the patient's stomach, there is no pain. In addition to the stomach, fiberoptic endoscopes can also get inside other important organs. On the one hand, the laser fiber endoscope can be used to check whether the patient's organs have lesions, but more importantly, it can input laser energy into the internal organs to irradiate the diseased tissues, i.e., to remove them, playing the role of a scalpel. Moreover, cutting with a laser knife, the wound can automatically stop bleeding, without the need to ligate the bleeding point, greatly shortening the operation time, the wound will not be inflamed. If you use the laser knife to remove malignant tumors, you can also prevent the spread of cancer cells.
(5) Laser Weapons
Laser missiles in the Gulf War, the U.S.-led multinational force launched large-scale air strikes into Iraqi territory, destroying many of Iraq's important military targets. In the end, the war ended in Iraq's defeat. Some people say that the Gulf War was a contest of advanced weapons, which is indeed true.
U.S. airplanes are equipped with laser sights that emit infrared lasers. When a reconnaissance aircraft in the air to find the ground target, the side in the air circling, while the laser sight constantly to the target to fire laser beams. This laser beam actually acts as a guide. At this point, other aircraft on attack missions then come in and drop laser-guided missiles on the target. These laser-guided missiles are equipped with an automatic tracking system. This automatic tracking system is equivalent to the eyes of the missile, when the missile swooped down to the target, it can be based on the guide laser reflected back from the target, constantly correct the course of flight, so as to hit the target accurately.
In fact, these laser-guided missiles were used by the United States in Vietnam as early as the 1970s. Now there are not only air-to-surface missiles, but also surface-to-surface, air-to-air and ground-to-air laser missiles.
Today, people have been able to combine radio search radar and laser radar to form combat systems. For example, when the radio radar discovers an air target (enemy aircraft or missile), it can accurately measure the target's altitude, bearing and speed. As soon as the target comes within a certain range, the laser radar will turn on and emit a very fine laser beam that stares at and accurately measures the position of the target, and then the laser missile, which is launched, will accurately hit the target and destroy it according to the guiding laser beam provided by the laser radar. These laser missiles can be easily deployed on trucks or converted into anti-tank missiles.
The anti-tank laser missiles that have been developed can be launched either from the ground or from a helicopter. The missiles are equipped with semiconductor lasers, which play a role in automatically tracking the target so that the missiles can hit the tanks with a hundred shots.
Laser radar, although high precision, small size, dexterous operation, easy to transfer, but it also has the disadvantage that it is easy to be restricted by meteorological conditions, and is not suitable for searching for targets in a wide range. Therefore, it is generally used in conjunction with the radio radar to complement each other.
Laser gun and laser gun so-called laser gun and laser gun are laser tactical weapons. They look like guns and cannons, but instead of bullets and shells, they fire laser beams to injure or blind enemy personnel. The amount of power of such guns and cannons is related to their own energy and firing distance. Right now, the effective range of laser guns and laser cannons is not far, so the power of deadlight is limited.
But the future of deadlight weapons is immeasurable. Once the energy of the laser beam is increased and the effective distance is increased, it will become a veritable dead light. For example, if a laser cannon is used to hit an airplane 10,000 meters in the air, it will take only one-thirty-thousandth of a second to hit the airplane because the forward speed of the laser beam is 300,000 kilometers per second. And in that short instant, the plane only has enough time to move forward a few centimeters in the air. In this way, for the dead light, the moving airplane actually becomes a dead target, and must die. According to this calculation, even if the missile is shot to thousands of kilometers away, the light of death only need to spend a few tenths of a second, and in this instant, the missile is only able to fly forward a few dozen meters. Therefore, Deadlight had ample time to destroy the missile in outer space.
In addition, lasers can constantly change direction, aiming at individual targets and destroying them one by one, and economically speaking, it is much cheaper to build laser cannons than it is to build intercontinental missiles.