brief introduction

The original Chinese names of LASER are "laser" and "laser", which are transliteration of its literary name, and abbreviations of English words amplified by stimulated emission. It means "optical amplification of stimulated radiation"

Laser power generation

If microscopic particles such as atoms or molecules have a high energy level E2 and a low energy level E 1, and the particle number densities of E2 and E 1 are N2 and N 1, there are three processes: spontaneous emission transition, stimulated emission transition and stimulated absorption transition. Stimulated emission light generated by stimulated emission transition has the same frequency, phase, propagation direction and polarization direction as incident light. So the stimulated emission of a large number of particles excited by the same coherent radiation field is coherent. The probability of stimulated emission transition and stimulated emission absorption transition is proportional to the monochromatic energy density of the incident radiation field. When the statistical weights of the two energy levels are equal, the probabilities of the two processes are equal. In the case of thermal equilibrium, N2 < N 1, so the stimulated absorption transition is dominant, and light usually attenuates due to stimulated absorption when passing through matter. The excitation of external energy can destroy the thermal balance and make N2 > N 1, which is called the population inversion state. In this case, stimulated emission transition is dominant. After the light passes through the laser working substance (active substance) with the length of L, the light intensity increases by eGl times. G is a coefficient directly proportional to (N2-N 1), which is called gain coefficient, and its size is also related to the properties of laser working medium and light wave frequency. One active substance is a laser amplifier.

If an activated substance is placed in an optical resonator composed of two parallel mirrors (at least one of which is partially transmissive) (Figure 1), high-energy particles will spontaneously emit in all directions. Among them, non-axial light waves quickly escape from the resonant cavity; However, the light wave propagating in the axial direction can propagate back and forth in the cavity, and the light intensity increases continuously when propagating in the laser material. If the unidirectional small signal gain G0l in the resonant cavity is greater than the unidirectional loss δ(G0 is the small signal gain coefficient), self-excited oscillation can occur. The motion state of atoms can be divided into different energy levels. When an atom jumps from a high energy level to a low energy level, it will release photons with corresponding energy (so-called spontaneous emission). Similarly, when a photon is incident on an energy-level system and absorbed by it, it will cause the atom to jump from a low energy level to a high energy level (so-called stimulated absorption); Then, some atoms that jump to the high energy level will jump to the low energy level and release photons (so-called stimulated radiation). These movements are not isolated, but often carried out simultaneously. When we create a condition, such as using a suitable medium, * * * cavity and enough external electric field, stimulated radiation will be amplified to be greater than stimulated absorption, then in general, photons will be emitted, thus generating laser.

Be irradiated by laser

What is "stimulated radiation"? It is based on a brand-new theory put forward by the great scientist Einstein in 19 16. This theory means that there are different numbers of particles (electrons) distributed in different energy levels in the atoms that make up matter. When a high-level particle is excited by a photon, it will jump from the high-level to the low-level level. At this time, they will emit light with the same properties as the light that excites them, and in a certain state, weak light can also excite strong light. This is called "optical amplification of stimulated radiation", or laser for short. Laser has four main characteristics: high brightness, high directivity, high monochromaticity and high coherence.

High brightness laser

The brightness of solid-state laser can be as high as1011w/cm2sr. Moreover, after the high-brightness laser beam is focused by the lens, it can produce thousands or even tens of thousands of degrees of high temperature near the focus, making it possible to process almost all materials.

High directivity of laser

The high directivity of laser makes it possible to effectively transmit long distances, and at the same time, it can ensure very high power density for focusing, both of which are important conditions for laser processing.

High monochromaticity of laser

Due to the high monochromaticity of laser, the beam can be accurately focused on the focus and high power density can be obtained.

High coherence of laser

Coherence mainly describes the phase relationship of each part of light wave. It is laser that has the above peculiar characteristics, so it has been widely used in industrial processing.

At present, laser has been widely used in laser welding, laser cutting and laser drilling (including oblique holes, irregular holes, gypsum holes, tipping paper holes, steel plate holes, packaging and printing holes, etc.). ), laser quenching, laser heat treatment, laser marking, glass carving, laser fine adjustment, laser lithography, laser film making, laser film processing, laser packaging, laser circuit repair, laser wiring technology, laser cleaning, etc.

After more than 30 years of development, lasers are almost everywhere now. It has been used in all aspects of life and scientific research: laser acupuncture, laser cutting, laser welding, laser quenching, CD, laser rangefinder, laser gyroscope, laser straightener, laser scalpel, laser bomb, laser radar, laser gun, laser cannon and so on. In the near future, lasers will definitely be more widely used.

Laser weapon is a kind of directional energy weapon, which directly destroys or paralyzes the target by using directional laser beam. According to different operational purposes, laser weapons can be divided into tactical laser weapons and strategic laser weapons. The weapon system is mainly composed of laser, tracking, aiming and launching devices. At present, the commonly used lasers are chemical lasers, solid-state lasers and CO2 lasers. Laser weapons have the advantages of fast attack speed, flexible steering, accurate attack and no electromagnetic interference, but they are also vulnerable to weather and environment. Laser weapon has a history of more than 30 years, and its key technology has also made a breakthrough. The United States, Russia, France, Israel and other countries have successfully carried out various laser shooting experiments. At present, low-energy laser weapons have been put into use, mainly used for short-range interference and blinding photoelectric sensors, as well as attacking human eyes and some enhanced observation equipment; High-energy laser weapons mainly use chemical lasers. According to the current level, it is expected to be deployed and used on ground and air platforms in the next 5- 10 years for tactical air defense, theater anti-missile and anti-satellite operations.

Other characteristics of laser

Laser has many characteristics: first, laser is monochromatic, or single frequency. Some lasers can produce lasers with different frequencies at the same time, but these lasers are isolated from each other and used separately. Secondly, the laser is coherent light. The characteristic of coherent light is that all its light waves are synchronous, and the whole beam of light is like a "wave train". Thirdly, laser is highly concentrated, that is, it needs a long distance to disperse or converge.

Laser is a kind of light source invented in 1960s. Laser is the abbreviation of stimulated emission amplification in English. There are many kinds of lasers, ranging in size from several football fields to a grain of rice or salt. Gas lasers include He-Ne lasers and argon lasers; Solid-state lasers include ruby lasers; Semiconductor lasers have laser diodes, such as CD players, DVD players and laser diodes in CD-ROMs. Each laser has its own unique method of generating laser.

Application of laser technology

Laser machining technology is a technology that uses the characteristics of the interaction between laser beam and substance, and takes cutting, welding, surface treatment, drilling, micromachining materials and identifying objects as light sources. The most traditional application field is laser processing technology. Laser technology is a comprehensive technology involving optics, mechanics, electricity, materials, detection and other disciplines. Traditionally, its research scope can be generally divided into:

Laser processing system. Comprise a laser, a light guide system, a processing machine tool, a control system and a detection system.

2. Laser processing technology. Including cutting, welding, surface treatment, drilling, marking, marking, fine tuning and other processing technologies.

Laser welding: automobile body thick plates, automobile parts, lithium batteries, pacemakers, sealed relays and other sealing devices, as well as various devices that are not allowed to weld pollution and deformation. At present, the lasers used are YAG laser, CO2 laser and semiconductor pump laser.

Laser cutting: cutting all kinds of metal parts and special materials in automobile industry, computer, electrical cabinet and woodworking tool mould industry, circular saw blade, acrylic, spring washer, copper plate of electronic parts below 2mm, partial metal mesh plate, steel pipe, tinned iron plate, lead-plated steel plate, phosphor bronze, bakelite plate, thin aluminum alloy, timely glass, silicone rubber and alumina ceramic plate 1mm or less. The lasers used are YAG laser and CO2 laser.

Laser marking: widely used in various materials and almost all industries. At present, the lasers used are YAG laser, CO2 laser and semiconductor pump laser.

Laser drilling: Laser drilling is mainly used in aerospace, automobile manufacturing, electronic instruments, chemical industry and other industries. The rapid development of laser drilling is mainly reflected in the increase of the average output power of YAG laser for drilling from 400w five years ago to 800w, reaching1000 W. At present, the more mature application of laser drilling in China is in the production of synthetic diamond and natural diamond wire drawing dies, as well as the production of gem bearings in industries such as clock instruments, aircraft blades and multilayer printed circuit boards. At present, most of the lasers used are YAG lasers and CO2 lasers, but there are also some excimer lasers, isotope lasers and semiconductor pump lasers.

Laser heat treatment: widely used in automobile industry, such as heat treatment of cylinder liner, crankshaft, piston ring, commutator, gear and other parts, as well as aerospace, machine tool industry and other mechanical industries. Laser heat treatment is widely used in China than abroad. At present, most of the lasers used are YAG laser and CO2 laser.

Laser rapid prototyping: it is formed by combining laser processing technology with computer numerical control technology and flexible manufacturing technology. Mostly used in mold and model industry. At present, most of the lasers used are YAG laser and CO2 laser.

Laser coating: widely used in aerospace, mold and electromechanical industries. At present, most of the lasers used are high-power YAG lasers and CO2 lasers.

Application of laser in medicine

Laser system applied to dentistry

According to the different functions of laser in dental application, it can be divided into several different laser systems. An important feature of distinguishing lasers is that the wavelength of light has different effects on tissues. Visible light and near infrared spectrum have low light absorption rate and strong penetration, and can penetrate deep tooth tissues, such as argon ion laser, diode laser or Nd: YAG laser (as shown in figure 1). However, Er: YAG laser and CO laser have poor light penetration, which can only penetrate the tooth tissue by about 0.01mm.. The second important feature that distinguishes laser is the intensity (i.e. power) of laser. For example, diode laser used for diagnosis is only a few milliwatts, and sometimes it can also be used for laser display.

The laser used for treatment is usually a moderate intensity laser of several watts. The effect of laser on tissue also depends on the way of laser pulse emission. Typical continuous pulse emission methods are argon ion laser, diode laser, CO2 laser and laser. Some Er: YAG lasers or many Nd: YAG lasers emit in short pulses. The intensity (i.e. power) of short-pulse laser can reach more than 1 1,000 watts. These high intensity and high light absorption lasers are only suitable for removing hard tissues.

Application of laser in the diagnosis of dental caries

1. Demineralization and shallow caries

2. Recessive dental caries

Application of laser in treatment

1. Cut

2. Filler polymerization and pit treatment

Laser beam weapon

Laser weapon is a kind of directional energy weapon, which directly destroys or paralyzes the target by using directional laser beam. According to different operational purposes, laser weapons can be divided into tactical laser weapons and strategic laser weapons. The weapon system is mainly composed of laser, tracking, aiming and launching devices. At present, the commonly used lasers are chemical lasers, solid-state lasers and CO2 lasers. Laser weapons have the advantages of fast attack speed, flexible steering, accurate attack and no electromagnetic interference, but they are also vulnerable to weather and environment. Laser weapon has a history of more than 30 years, and its key technology has also made a breakthrough. The United States, Russia, France, Israel and other countries have successfully carried out various laser shooting experiments. At present, low-energy laser weapons have been put into use, mainly used for short-range interference and blinding photoelectric sensors, as well as attacking human eyes and some enhanced observation equipment; High-energy laser weapons mainly use chemical lasers. According to the current level, it is expected to be deployed and used on ground and air platforms in the next 5- 10 years for tactical air defense, theater anti-missile and anti-satellite operations.

Laser history

1958, American scientists Luo Xiao and Downs discovered a magical phenomenon: when they shine the light from the inner bulb on the rare earth crystal, the molecules of the crystal will emit bright light, and these lights will always gather together. According to this phenomenon, they put forward the "laser principle", that is, when a substance is excited by the same energy as its molecular natural oscillation frequency, it will produce this indiscriminate strong light-laser. They found important documents for this.

After the publication of the research results of Xiao Luo and Downs, scientists from all over the world put forward various experimental schemes, but none of them succeeded. 1960 on may 15, a scientist at Hughes laboratory in California announced that he had obtained a laser with a wavelength of 0.6943 micron, which was the first laser ever obtained by mankind, and thus became the first scientist in the world to introduce laser into practical fields.

1960 On July 7th, Mayman announced the birth of the world's first laser. Meman's plan is to use a high-intensity flash tube to excite the chromium atoms in the ruby crystal, thus producing a fairly concentrated slender red beam, which can reach a higher temperature than the surface of the sun when it hits a certain point.

Former Soviet scientist H.γ. Basov invented the semiconductor laser in 1960. The structure of semiconductor laser is usually composed of P layer, N layer and active layer, forming a double heterojunction. Its characteristics are: small volume, high coupling efficiency, fast response, wavelength and size suitable for fiber size, direct modulation and good coherence.

The new progress of laser research in China is of great significance to military science.

According to the Chinese Academy of Sciences, through the efforts of the R&D team of the Institute of Physics of the Chinese Academy of Sciences, the direct measurement of large-area excimer laser energy has been realized for the first time, and the effective measurement diameter is 100mm, which is the largest pyroelectric laser detector in the world at present. The cooperation with experts from China Institute of Atomic Energy and the experiments in the national laboratory show that the system has reached the expected technical indicators in different energy regions (10-20J and 100-200mJ).

According to reports, laser fusion research is a promising energy development topic, and laser-controlled thermonuclear fusion reaction will surely bring a new turning point to human life. Laser fusion is also of great significance in military scientific research. In the laser fusion experiment, especially in the research of indirect drive fusion, people pursue high X-ray conversion efficiency, good radiation transport environment and the best radiation driving field to produce strong radiation driving field. It is very important to directly monitor and study the energy of excimer laser in these research processes.

The research results show that the research and development of this project not only has the strength to continuously explore the developed product market, but also has the ability to undertake and develop the application demand projects being developed by the country.

The "laser revolution" is of great significance.

In modern society, information plays an increasingly important role. The faster, more accurate and richer the information, the more active the initiative and the more chances of success. The appearance of laser triggered an information revolution. From VCD and DVD discs to laser phototypesetting, the use of laser greatly improves efficiency and facilitates people to save and extract information. The "laser revolution" is of great significance. Laser has good space control and time control, and has great freedom for the material, shape, size and processing environment of the processed object, which is especially suitable for automatic processing. The combination of laser processing system and computer numerical control technology can form efficient automatic processing equipment, become the key technology for enterprises to implement timely production, and open up broad prospects for high-quality, efficient and low-cost processing and production. At present, laser technology has been integrated into our daily life, and in the years to come, laser will bring us more miracles.

Laser is a new modern light source, which has the characteristics of good directivity, high brightness and good monochromaticity. It is widely used, such as laser ranging, laser drilling and cutting, earthquake monitoring, laser surgery, laser singing head and so on. The unique ablation effect, shock wave effect and radiation effect produced by laser weapons have been widely used in air defense, anti-tank and bomber, and have shown their magical power. There are two leading companies in China's laser industry, Hanzu Laser in the south and G Keda (600986) in the north. Interestingly, the circulation of these two laser stocks is only 54.68 million shares and 49.53 million shares respectively, both of which are pocket-sized, but the share price of G University of Science and Technology is not as small as that of Hanzu Laser, so it has strong explosive potential in the future. G Kodak's main business is laser electronic products. The company cooperates with foreign capital to produce laser heads and related electronic products with international advanced technology level. The company has installed and operated 24 production lines, producing three types and multiple models of laser heads, and can process 48 million pieces of various laser heads every year, becoming the largest laser head production base in China and competing with the "big laser family" in the industry. Dongying Keying Laser Electronics Co., Ltd., a holding subsidiary of G Keda, is engaged in the production and sales of electronic laser heads, movements and related products. The leading product, digital decoding laser head, is widely used in high-tech electronic products such as computers, DVD players and game machines. At present, the main customers are LG Electronics, Asus Computer, Jianxing Electronics and other well-known IT manufacturers. Because the laser head and its series products condense the essence of high-tech such as optics, electronics, precision machinery, microcomputer, new materials and micro-processing, it is the most modern.

In addition, Keda Industry, the parent company of G Keda, promised in its 2005 annual report that the "Qingdao Low-temperature and Atmospheric LPG Storage and Transportation Project" will be injected into listed companies after completion, so that G Keda will hold the largest LPG base project in East China and create huge profit growth points. Because LPG is a seller's market, the price may soar and the company's development prospects will be first-class. G Kodak and Han's Laser are two giants of laser electronics in China, and they are forming two fist industries of laser and liquefied petroleum gas construction projects. Especially after the injection of liquefied petroleum gas project, the company's performance will increase substantially. At present, there are less than 50 million shares in circulation, and the share price is near the net asset value, far from the issue price of 8.6 yuan, which has good investment speculation value. Recently, the main force has been heavily involved in bargain hunting, and the market outlook is expected to disappear, which deserves close attention. Laser science is a new discipline developed in 1960s, and it is one of the major scientific and technological achievements after atomic energy, computer and semiconductor technology.

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