Laser's original Chinese name is called "laser", "LASER", is its English name LASER phonetic translation, is taken from the English Light Amplification by Stimulated Emission of Radiation is taken from the English Light Amplification by Stimulated Emission of Radiation of the words of the first letter of the acronym. It means "Light Amplification by Stimulated Emission of Radiation". The full name of the laser in English has fully expressed the main process of manufacturing lasers. 1964 in accordance with China's famous scientists Qian Xuesen suggested that the "light stimulated emission" renamed "laser".
Laser is the 20th century, following atomic energy, computers, semiconductors, mankind's another major invention, known as the "fastest knife", "the most accurate ruler", "the brightest light "and the "strange laser". Its principle was discovered by the famous physicist Albert Einstein as early as 1916, but it was not until 1958 that lasers were successfully manufactured for the first time. The laser came into being against the background of theoretical preparations and the urgent need for production practice, and as soon as it was introduced, it gained extraordinary rapid development, which not only gave new life to the ancient science and technology of optics, but also led to the emergence of an entire new industry. Lasers enable people to effectively utilize unprecedented advanced methods and means to obtain unprecedented benefits and results, thus promoting the development of productivity.
Laser generation
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If the atom or molecule and other microscopic particles with high energy level E2 and low energy level E1, E2 and E1 energy levels on the Bouygues number density of N2 and N1, in the two levels of the existence of a spontaneous emission of leaps, stimulated emission of leaps and excited absorption of leaps and so on the three processes. The stimulated emission light produced by the stimulated emission jump has the same frequency, phase, propagation direction and polarization direction as the incident light. Therefore, the stimulated emitted light produced by a large number of particles excited by the same coherent radiation field is coherent. Both the stimulated emission jump probability and the stimulated absorption jump probability are proportional to the monochromatic energy density of the incident radiation field. When the statistical weights of the two energy levels are equal, the chances of the two processes are equal. In thermal equilibrium N2 < N1, so excited absorption leaps dominate and light passing through matter is usually attenuated by excited absorption. The excitation of external energy can destroy the thermal equilibrium and make N2 > N1,this state is called the particle number reversal state. In this case, excited emission leaps dominate. Light through a section of the length of l in the particle number reversal state of the laser working material (activated material), the light intensity increases eGl times. G is proportional to the (N2-N1) coefficient, known as the gain coefficient, the size of the laser working material with the nature of the light and the frequency of light waves related. A section of activated material is a laser amplifier.
If, for example, a section of activated matter is placed in an optical resonance cavity consisting of two mirrors parallel to each other, at least one of which is partially transmissive (Fig. 1), particles at higher energy levels produce spontaneous emission in various directions. Non-axially propagating light waves quickly escape from the cavity: axially propagating light waves can travel back and forth within the cavity, and the intensity of the light grows as it propagates through the laser material. If the one-way small-signal gain G0l in the resonant cavity is greater than the one-way loss δ (G0l is the small-signal gain coefficient), self-excited oscillations can be generated. The state of motion of an atom can be divided into different energy levels, and when an atom leaps from a high energy level to a low energy level, it releases a photon of the corresponding energy (so-called spontaneous radiation). Similarly, when a photon is incident on and absorbed by a system of energy levels, it causes the atom to jump from a lower to a higher energy level (so-called stimulated absorption); the atom that has partially jumped to a higher energy level then jumps to a lower energy level and releases a photon (so-called stimulated radiation). These movements are not isolated, but are often simultaneous. When we create conditions, such as a suitable medium, a *** vibration cavity, and a sufficient external electric field, where the excited radiation is amplified so that it is more than the excited absorption, then overall, photons will be emitted, resulting in a laser.
Characteristics of lasers
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(a) Directional emission
Ordinary light sources emit light in all directions. To allow the emitted light to propagate in one direction, it is necessary to equip the light source with a certain light-gathering device, such as the car's headlights and searchlights are installed with a light-gathering effect of the reflector, so that the radiated light is pooled to shoot in one direction. Laser emitted by the laser, inherently is shot in one direction, the dispersion of the beam is extremely small, about only 0.001 radians, close to parallel. 1962, mankind's first use of laser irradiation of the moon, the Earth's distance from the moon is about 380,000 kilometers, but the laser on the surface of the moon's light spot less than two kilometers. If the spotlight effect is very good, seemingly parallel searchlight light column shot to the moon, according to its spot diameter will cover the entire moon.
(B) very high brightness
Before the invention of the laser, the artificial light source in the high-pressure pulsed xenon lamp has the highest brightness, and the sun's brightness is not comparable to the ruby laser laser brightness, can be more than xenon lamps tens of billions of times. Because lasers are so bright, they are able to illuminate objects at great distances. The beam emitted by a ruby laser produces an illumination on the Moon of about 0.02 lux (the unit of light intensity), with a bright red color and a clearly visible laser spot. If the moon is illuminated by the most powerful searchlight, the illumination produced is only about one trillionth of a lux, which is undetectable to the human eye. The main reason for the extreme brightness of the laser is directional luminescence. A large number of photons are concentrated in a very small area of space, and the energy density is naturally very high.
(C) the color is extremely pure
The color of light by the wavelength (or frequency) of light. A certain wavelength corresponds to a certain color. Sunlight wavelength distribution range of about 0.76 microns to 0.4 microns, corresponding to the color from red to purple **** 7 colors, so the sunlight can not talk about monochromatic. Light sources that emit a single color of light are called monochromatic light sources, which emit a single wavelength of light waves. For example, krypton, helium, neon, and hydrogen lamps are monochromatic light sources that emit only one color of light. Monochromatic light source light wavelengths, although a single, but there is still a certain range of distribution. Such as krypton lamp only emits red light, monochromaticity is very good, known as the crown of monochromaticity, the range of wavelength distribution is still 0.00001 nanometers, so krypton lamps emit red light, if carefully identified still contains dozens of red. It can be seen that the narrower the wavelength distribution interval of light radiation, the better the monochromaticity.
Laser output light, wavelength distribution range is very narrow, so the color is extremely pure. To output red light of helium-neon laser, for example, the wavelength distribution range of its light can be as narrow as 2 × 10-9 nanometers, is krypton lamp emitted by the red light wavelength distribution range of two millionths. This shows that the monochromaticity of the laser far exceeds that of any monochromatic light source.
In addition, the laser has other characteristics: good coherence. Laser frequency, vibration direction, phase is highly consistent, so that the laser light waves overlap in space, the distribution of light intensity in the overlap zone will appear stable strength of the phenomenon. This phenomenon is called light interference, so the laser is coherent light. And ordinary light source issued by the light, its frequency, vibration direction, phase is not consistent, called non-coherent light.
The flash time can be extremely short. Due to technical reasons, the flash time of ordinary light sources can not be very short, the flash lamp used for photography, the flash time is about one-thousandth of a second. Pulsed laser flash time is very short, can reach 6 femtoseconds (1 femtosecond = 10-15 seconds). Light sources with very short flash times have important uses in production, scientific research and the military.
(D) great energy density
Photon energy is calculated using E = hf, where h is Planck's constant, f for the frequency. It can be seen that the higher the frequency, the higher the energy. Laser frequency ranges from 3.846*10^(14)Hz to 7.895*10^(14)Hz.The electromagnetic spectrum can be roughly divided into: (1) radio waves - wavelengths from a few kilometers to about 0.3 meters, which are generally used in the bands of television and radio broadcasting; (2) microwaves -wavelength from 0.3 meters to 10-3 meters, these waves are mostly used in radar or other communication systems; (3) infrared - wavelength from 10-3 meters to 7.8 × 10-7 meters; (4) visible light - -this is the light that people can sense. -This is an extremely narrow band of light that people can sense. The wavelength ranges from 780-380 nm.Light is an electromagnetic wave emitted when the electrons within an atom or molecule change their state of motion. Since it is a very small portion of electromagnetic waves that we can directly feel and perceive; (5) Ultraviolet light - wavelengths from 3 × 10-7 meters to 6 × 10-10 meters. These waves are produced for similar reasons as light waves and are often emitted during electrical discharges. Since its energy is comparable in magnitude to the energy involved in a typical chemical reaction, the chemical effects of ultraviolet light are the strongest; (6) roentgen rays- This portion of the electromagnetic spectrum, with wavelengths ranging from 2 × 10-9 meters to 6 × 10-12 meters. Roentgen rays (X-rays) are emitted when the inner electrons of an electric atom jump from one energy state to another or when the electrons decelerate within the electric field of the nucleus; (7) γ-rays - are electromagnetic waves with wavelengths from 10-10 to 10-14 meters. This invisible electromagnetic waves are emitted from the atomic nucleus, radioactive substances or atomic nuclear reactions are often accompanied by the emission of this radiation. γ-rays are very penetrating, very destructive to living beings. From this point of view, the laser energy is not very large, but its energy density is very large (because of its small range of action, usually only a point), a short period of time to gather a large amount of energy, used as a weapon is also understandable.
Stimulated radiation
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What is "stimulated radiation"? It is based on a completely new theory proposed by the great scientist Albert Einstein in 1916. This theory is that in the composition of matter in the atom, there are a different number of particles (electrons) distributed in different energy levels, the particles in the high energy level by some kind of photon excitation, will be from the high energy level to jump (jump) to the low energy level, this time it will be radiated with the excitation of the light of the same nature of the light, but also in a certain state, there can be a weak light excitation of the phenomenon of a strong light. This is called "light amplification by excited radiation", referred to as laser. Laser has four main characteristics: laser brightness, high directionality, high monochromaticity and high coherence.
At present, laser has been widely used in laser welding, laser cutting, laser punching (including diagonal holes, different holes, plaster punching, cork paper punching, steel punching, packaging and printing holes, etc.), laser quenching, laser heat treatment, laser marking, glass engraving, laser fine-tuning, laser lithography, laser film, laser thin film processing, laser encapsulation, laser circuit repair, laser wiring technology, laser cleaning, and so on. cleaning, etc.
After more than 30 years of development, laser is now almost everywhere, it has been used in all aspects of life, scientific research: laser acupuncture, laser cutting, laser cutting, laser welding, laser quenching, laser records, laser rangefinders, laser gyroscope, laser straightener, laser scalpel, laser bombs, LIDAR, laser guns, laser guns.... ..., in the near future, laser will certainly have a wider range of applications.
Other properties of lasers
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Lasers have many properties: first, lasers are monochromatic, or single-frequency. There are lasers that can produce lasers of different frequencies at the same time, but these lasers are isolated from each other and used separately. Second, lasers are coherent light. Coherent light is characterized by the fact that all its light waves are synchronized, and the whole beam of light is like a "wave train". Again, laser light is highly concentrated, meaning it has to travel a long distance before it disperses or converges.
Lasers (LASER) are a type of light source invented in the 1960s; LASER is an acronym for Light Amplification by Stimulated Emission. There are many types of lasers, ranging in size from a few soccer fields to a grain of rice or a grain of salt. Gas lasers are helium-neon lasers and argon lasers; solid-state lasers are ruby lasers; and semiconductor lasers are laser diodes, like those found in CD players, DVD players, and CD-ROMs. Each type of laser has its own unique method of generating laser light.
Laser technology applications
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Laser processing technology is the use of laser beams and material interaction characteristics of the material (including metal and non-metal) for cutting, welding, surface treatment, punching, micromachining, and as a source of light, identification of objects, etc., a technology, the traditional application of the largest field of laser processing technology. Laser technology is involved in light, machine, electricity, materials and testing and other disciplines of a comprehensive technology, traditionally, the scope of its research can generally be divided into:
1. laser processing system. Including lasers, light guide system, processing machine tools, control systems and detection systems.
2. Laser processing process. Including cutting, welding, surface treatment, punching, marking, scribing, fine-tuning and other various processing processes.
Laser welding: auto body thick and thin plates, automotive parts, lithium batteries, pacemakers, sealed relays and other sealed devices, as well as a variety of devices that do not allow welding contamination and deformation. Currently used lasers are YAG lasers, CO2 lasers and semiconductor pumped lasers.
Laser cutting: automotive industry, computers, electrical chassis, wood knife mold industry, a variety of metal parts and special materials, cutting, circular saw blades, acrylic, spring gaskets, 2mm or less of the electronic parts with copper, some metal mesh board, steel pipe, tin-plated iron plate, lead-plated steel, phosphor bronze, bakelite, thin aluminum alloys, quartz glass, silicone rubber, alumina ceramic sheet 1mm or less, Titanium alloy used in the aerospace industry and so on. The lasers used are YAG laser and CO2 laser.
Laser marking: in a variety of materials and almost all industries are widely used, the current use of lasers are YAG lasers, CO2 lasers and semiconductor pump lasers.
Laser perforation: laser perforation is mainly used in aerospace, automobile manufacturing, electronic instrumentation, chemical industry. The rapid development of laser perforation, mainly reflected in the perforation of the average output power of YAG lasers has been increased from 400w 5 years ago to 800w to 1,000w. Domestic more mature laser perforation applications are in the production of synthetic diamond and natural diamond wire drawing die and clocks and instruments, gemstone bearings, aircraft blades, multi-layer printed wiring boards, and other industries in the production. Most of the lasers used today are YAG lasers and CO2 lasers, but there are also some excimer lasers, isotope lasers and semiconductor pumped lasers.
Laser heat treatment: widely used in the automotive industry, such as cylinder liners, crankshafts, piston rings, commutators, gears and other parts of the heat treatment, but also in the aerospace, machine tool industry and other machinery industry is also widely used. China's laser heat treatment applications are far more extensive than abroad. The current use of lasers are mostly YAG lasers, CO2 lasers are mainly.
Laser rapid prototyping: laser processing technology and computer numerical control technology and flexible manufacturing technology combined and formed. Mostly used in molds and models industry. Currently using the laser is mostly YAG laser, CO2 laser-based.
Laser coating: widely used in aerospace, mold and die and electromechanical industries. Currently used lasers are mostly high-power YAG lasers, CO2 lasers are mainly.