He-Ne laser: the most important red radiation source (632.8 nm).
Carbon dioxide laser: The wavelength is about 10.6 micron (infrared), which is an important industrial laser.
Carbon monoxide laser: The wavelength is about 6-8 microns (infrared), and it only works under cooling conditions.
Nitrogen laser: 337. 1 nanometer (ultraviolet).
Argon ion laser: It has multiple wavelengths, 457.9 nm (8%), 476.5 nm (12%), 488.0 nm (20%), 496.5 nm (12%) and 5065438.
Helium cadmium laser: the most important blue light (442 nm) and near ultraviolet laser source (325 nm).
Krypton ion laser: There are multiple wavelengths, 350.7nm, 356.4nm, 476.2nm, 482.5nm, 520.6nm, 530.9nm, 586.2nm, 647. 1nm (the strongest).
Oxygen ion laser
Xenon ion laser
Mixed gas laser: it does not contain pure gas, but a mixture of several gases (generally argon, krypton, etc.). ).
Excimer laser: KrF (248 nm), XeF (35 1-353 nm), ArF (193 nm), XeCl (308 nm), F2 (157 nm).
Metal vapor laser: such as copper vapor laser, with wavelength between 5 10.6-578.2 nm. Because it has a good reinforcing effect, there is no need to use a resonant mirror.
Metal halide laser: such as copper bromide laser, the wavelength is between 5 10.6-578.2 nm. Because it has a good reinforcing effect, there is no need to use a resonant mirror.
Chemically excited laser is a special form. Excitation is carried out through chemical reactions in the medium. The medium is disposable and is consumed after use. Very suitable for high-power conditions and military fields.
Hydrochloride laser
The medium of iodine laser is solid-state laser, which is pumped and excited by lasers such as lamps and semiconductor laser arrays. Thermal lens effect is the defect of most solid-state lasers.
Ruby laser: the first laser in the world, 1960. On July 7th, American young scientist Mayman announced the birth of the world's first laser. This laser is a ruby laser, with a working wavelength of 6943, single pulse and output energy of1ms.
Nd:YAG: The most commonly used solid-state laser works at 1064nm, which is a four-level system. There are other energy levels that can output lasers with other wavelengths.
Nd:YVO4 _ 4 (neodymium-doped yttrium vanadate): the most widely used low-power solid-state laser. Its working wavelength is generally 1064nm, and it can generate 532nm green light after frequency doubling by KTP and LBO nonlinear crystals.
Yb:YAG (Yb-doped yttrium aluminum garnet): It is suitable for high power output, and the disk laser made of this material has a strong advantage in the field of laser industrial processing.
Ti: sapphire laser: wide wavelength adjustment range (670 nm ~ 1200 nm).
Semiconductor laser is also called semiconductor laser diode, or LD for short. Because of the particularity of the material structure of the semiconductor material itself and the particularity of the movement law of electrons in the semiconductor material, the working characteristics of the semiconductor laser have its particularity. Semiconductor laser is a device that uses a certain semiconductor material as its working substance to produce stimulated emission. Its working principle is to realize the population inversion of unbalanced carriers between the energy bands (conduction band and valence band) of semiconductor substances or between the energy bands of semiconductor substances and the energy levels of impurities (acceptors or donors) through a certain excitation mode. Stimulated emission occurs when a large number of electrons in the state of population inversion recombine with holes. There are three main excitation modes of semiconductor lasers, namely electric injection, optical pumping and high energy electron beam excitation. Electroinjection semiconductor lasers are generally semiconductor junction diodes made of gallium arsenide (GaAs), cadmium sulfide (CdS), indium phosphide (InP), zinc sulfide (ZnS) and other materials, which are excited by forward bias injection current and produce stimulated emission in the junction plane region. Optically pumped semiconductor lasers generally use n-type or p-type semiconductor single crystals (such as GaAS, InAs, InSb, etc. ) As a working substance, lasers emitted by other lasers are excited as optical pumps. Semiconductor lasers excited by high-energy electron beams generally use N-type or P-type semiconductor single crystals (such as PbS, CdS, ZhO, etc.). ) as a working substance and excited by injecting high-energy electron beams from the outside. Among semiconductor lasers, the double heterostructure electrically injected GaAs diode laser has better performance and wider application. Semiconductor lasers are pumped by injecting current. The wavelength range of semiconductor laser is from ultraviolet to infrared (300nm~ to more than ten microns), in which 1.3um and 1.55um are two windows of optical fiber transmission. Semiconductor laser has the outstanding characteristics of high energy conversion efficiency, easy high-speed current modulation, ultra-miniaturization, simple structure and long life, which makes it the most important and valuable laser. Semiconductor laser is a kind of laser which matures earlier and develops faster. Because of its wide wavelength range, simple manufacture, low cost and easy mass production, and because of its small size, light weight and long service life, its varieties have developed rapidly, and its application range has exceeded 300. The main application field of semiconductor laser is Gb LAN, and the semiconductor laser with 850nm wavelength is suitable for) 1Gh/. Local area network, semiconductor laser with wavelength of 1300nm-1550nm is suitable for 10gb local area network system. The application of semiconductor laser covers the whole field of optoelectronics and has become the core technology of optoelectronics. Semiconductor lasers are used in laser ranging, laser radar, laser communication, laser simulation weapons, laser early warning, laser guidance and tracking, ignition and initiation, automatic control and so on. From 65438 to 0978, semiconductor lasers began to be used in optical fiber communication systems. Semiconductor laser can be used as the light source and indicator of optical fiber communication, and the photoelectric subsystem can be formed by large-scale integrated circuit plane technology. Because of the excellent characteristics of semiconductor laser, such as ultra-miniaturization, high efficiency and high speed operation, the development of such devices has been closely combined with optical communication technology from the beginning. It plays an important role in optical communication, optical transformation, optical interconnection, parallel optical wave system, optical information processing and storage, and optical disaster of optical computer peripheral equipment. The advent of semiconductor laser has greatly promoted the development of information photoelectric technology, and now it has become the fastest developing and most important laser optical fiber communication light source in the field of optical communication. The combination of semiconductor laser and low-loss optical fiber has a great influence on optical fiber communication and accelerated its development. So, you can use it. Double heterojunction laser is an important light source for optical fiber communication and atmospheric communication. Nowadays, distributed feedback semiconductor laser (DFB-LD) is used in all long-distance and large-capacity optical information transmission systems. Semiconductor lasers are also widely used in optical disc technology, which is a comprehensive technology integrating computing technology, laser technology and digital communication technology. It is a large-capacity, high-density, fast, effective and low-cost information storage means, which requires the light beam generated by the semiconductor laser to read and write information.
motivation model
① Optically pumped laser. Refers to the laser excited by optical pump, including almost all solid-state lasers and liquid lasers, as well as a few gas lasers and semiconductor lasers. ② Electro-excited laser. Most gas lasers are excited by gas discharge (DC discharge, AC discharge, pulse discharge and electron beam injection), while most common semiconductor lasers are excited by junction current injection, and some semiconductor lasers can also be excited by high energy electron beam injection. ③ Chemical laser. This refers to the laser that uses the energy released by chemical reaction to excite the working substance. The chemical reactions produced by reflection can be initiated by light, discharge and chemistry respectively. (4) nuclear pump laser. It refers to a special laser that uses the energy released by small nuclear fission reaction to excite working substances, such as nuclear pump He-Ar laser.
Mode of operation
Due to the different working materials, excitation methods and application purposes, the working modes and working states of lasers are also different, which are mainly divided into the following categories. (1) CW laser is characterized by the excitation of working substance and the corresponding laser output, which can be continuously carried out in a long time range. Solid-state lasers excited by continuous light sources, gas lasers and semiconductor lasers working in continuous electric excitation mode all belong to this category. Because the device will inevitably produce overheating effect in the process of continuous operation, most devices need to take appropriate cooling measures. (2) Single pulse laser. For this kind of laser, the excitation of the working substance and the corresponding laser emission are both a single pulse process in time. General solid-state lasers, liquid lasers and some special gas lasers all work in this way. At this time, the thermal effect of the device can be ignored, so no special cooling measures can be taken. (3) Repetitive pulse laser, characterized in that its output is a series of repeated laser pulses. Therefore, the device can be excited by repetitive pulses, or it can be excited in a continuous manner, but the laser oscillation process is modulated in a certain way to obtain repetitive pulse laser output. Usually, the equipment also needs effective cooling measures. ④ Q-switched laser refers to a pulse laser with a certain switching technology to obtain a higher output power. Its working principle is: after the inversion of the number of particles in the working medium is formed, laser oscillation does not occur (the switch is in the closed state), and when the number of particles accumulates to a high enough level, the switch is suddenly turned on, thus forming a strong laser oscillation in a short time (such as 10 ~ 10 second). Laser tuning technology). ⑤ Mode-locked laser is a special type of laser using mode-locked technology, which is characterized by a definite phase relationship between different longitudinal modes in the * * resonant cavity, so a series of laser ultrashort pulse sequences (pulse width 10 ~ 10 second) with equal time intervals can be obtained. If the special fast optical switching technology is further adopted, a single ultrashort laser pulse can be selected from the above pulse sequence. ⑥ Single mode and frequency stabilized lasers. Single-mode laser refers to a laser that works in a single transverse mode or a single longitudinal mode after adopting certain mode-limiting technology. Frequency-stabilized laser refers to a special laser device that uses certain automatic control measures to stabilize the output wavelength or frequency of the laser within a certain precision range. In some cases, they can also be made into special laser devices with single-mode operation and automatic frequency stabilization control ability (see laser frequency stabilization technology). ⑦ Tunable lasers, generally speaking, the output wavelength of lasers is fixed, but after adopting special tuning technology, the output laser wavelength of some lasers can be continuously and controllably changed within a certain range. This kind of laser is called tunable laser (see laser tuning technology).
Band range
According to the different wavelength range of output laser, various lasers can be divided into the following types. (1) far infrared laser, the output wavelength range is between 25 ~ 1000 micron, and the laser output of some molecular gas lasers and free electron lasers belong to this region. ② Mid-infrared laser refers to a laser device whose output laser wavelength is in the mid-infrared region (2.5 ~ 25 microns), which represents CO2 molecular gas laser (10.6 microns) and CO molecular gas laser (5 ~ 6 microns). (3) Near-infrared laser refers to a laser device whose output laser wavelength is in the near-infrared region (0.75 ~ 2.5 microns), represented by Nd-doped solid-state laser (1.06 microns), CaAs semiconductor diode laser (about 0.8 microns) and some gas lasers. ④ Visible laser refers to a kind of laser device whose output laser wavelength is in the visible spectrum region (4,000 ~ 7,000 angstrom or 0.4 ~ 0.7 micron), including ruby laser (6,943 angstrom), He-Ne laser (6,328 angstrom), argon ion laser (4,880 angstrom, 5 145 angstrom) and krypton ion laser (4,743 angstrom). ⑤ Near-ultraviolet laser, whose output laser wavelength ranges from 2000 to 4000 angstrom, is composed of nitrogen molecular laser (337 1 angstrom), xenon fluoride (XeF) excimer laser (351angstrom, 353 1 angstrom), krypton fluoride. ⑥ Vacuum ultraviolet laser, whose output laser wavelength range is in the vacuum ultraviolet spectrum region (50 ~ 2000 angstrom), represented by (h) molecular laser (1644 ~ 1098 angstrom), xenon (Xe) excimer laser (1730 angstrom), etc. ⑦X-ray laser refers to a laser system whose output wavelength is in the X-ray spectral region (0.0 1 ~ 50 A). Soft X-ray has been successfully developed, but it is still in the exploration stage.
Historical origin
The invention of laser is a great achievement of science and technology in the 20th century. Finally, people can drive the luminescence process of molecules and atoms with extremely small scale, large quantity and chaotic motion, so as to obtain the ability to generate and amplify coherent infrared rays, visible rays and ultraviolet rays (even X rays and γ rays). With the rise of laser science and technology, human understanding and utilization of light has reached a new level. The birth history of laser can be roughly divided into several stages, among which the concept of stimulated radiation put forward by Einstein in 19 16 is an important theoretical basis. This theory points out that a matter particle in a high-energy state will be transformed into a low-energy state under the action of a photon whose energy is equal to the energy difference between two energy levels, and a second photon will be generated and emitted at the same time as the first photon, which is stimulated radiation. The light output by this radiation is amplified and coherent, that is, the emission direction, frequency, phase and polarization of multiple photons are exactly the same.
stage of development
Since then, the establishment and development of quantum mechanics have made people have a deeper understanding of the microstructure and motion law of matter, and the energy level distribution, transition and photon radiation of microscopic particles have also been more strongly proved, objectively perfecting Einstein's stimulated radiation theory and further laying a theoretical foundation for the generation of laser. After its birth in the late 1940s, quantum electronics was quickly applied to study the interaction between electromagnetic radiation and various micro-particle systems, and many corresponding devices were developed. The rapid development of these scientific theories and technologies has created conditions for the invention of laser.
If there are more particles in high energy state than in low energy state in a system, there will be particle number inversion. So as long as there is a photon, it will force an atom in a high energy state to emit a photon like it, and these two photons will cause other atoms to emit stimulated radiation, thus realizing the amplification of light; If the feedback effect of the appropriate resonant cavity is added, optical oscillation will be formed and laser will be emitted. This is how lasers work. 195 1 year, American physicists purcell and Pound successfully caused the inversion of the number of particles in the experiment and obtained stimulated radiation of 50 kHz per second. Later, American physicist Charles Downes and Soviet physicists Massoff and ProHohloff successively put forward the design of generating and amplifying microwave by using the principle of atomic and molecular stimulated radiation.
However, most of the above theoretical and experimental studies of microwave spectroscopy belong to "pure science", and whether the laser can be developed successfully was still very slim at that time.
Mature stage
But the scientists' efforts finally paid off. 1954, Thomas, the American physicist mentioned earlier, finally made the first ammonia molecular beam maser, which successfully set a precedent for using molecular and atomic systems as coherent amplifiers or oscillators for microwave radiation.
The maser developed by Downs et al. only produces microwaves with the wavelength of 1.25 cm, and the power is very small. With the development of production and technology, scientists are urged to explore new luminous mechanisms to produce new light sources with excellent performance. 1958, Downs and his brother-in-law, Arthur Sholow, combined the maser with the theoretical knowledge of optics and spectroscopy, and put forward the key proposal of adopting an open resonator, which prevented the characteristics of laser such as coherence, directivity, linewidth and noise. At the same time, Basov, ProHohloff and others also put forward the principle scheme to realize the optical amplification of stimulated radiation.
Since then, many laboratories in the world have participated in a fierce development competition to see who can successfully manufacture and operate the world's first laser.
1960, American physicist Theodore Mayman won the global development competition with a slight advantage in his research laboratory in Miami, Florida. He used a high-intensity flash tube to stimulate the chromium atoms in the ruby crystal, thus producing a fairly concentrated slender red beam, which can reach a higher temperature than the sun when it hits a certain point.
The "Meman design" has aroused the shock and suspicion of the scientific community, because scientists have been waiting and looking forward to the He-Ne laser.
Although Maiman was the first scientist to introduce laser into the practical field, the debate in court about who invented this technology once caused great controversy. One of the competitors is Gordon Gould, who invented "laser" (short for stimulated emission optical frequency amplifier). This word was put forward when he was a Ph.D. student at 1957 Columbia University. At the same time, the inventors of maser Towns and Sholow also developed the concept of laser. After the final judgment of the court, Downs became the winner, because the written work of the research was nine months earlier than Gould's. However, the invention right of Maiman Laser has not been shaken.
196065438+In February, an American scientist of Iranian origin, Jia Wan, led people to finally successfully manufacture and operate the world's first gas laser-He-Ne laser. 1962, three groups of scientists invented the semiconductor laser almost simultaneously. 1966, scientists developed an organic dye laser with continuously adjustable wavelength in a certain range. In addition, there are chemical lasers with large output energy, high power and independent of power grid.
Main applications
Laser is one of the essential core components in modern laser processing system. With the development of laser processing technology, lasers are also developing constantly, and many new lasers have appeared. The early lasers used for laser processing were mainly high-power CO2 gas lasers and lamp-pumped solid-state YAG lasers. From the development history of laser processing technology, the first laser appeared in the mid-1970s, which was a sealed CO2 laser tube. So far, the fifth generation CO2 laser-diffusion-cooled CO2 laser has appeared. It can be seen from the development that the early CO2 lasers tend to increase the laser power. However, when the laser power reaches a certain requirement, the beam quality of the laser is paid attention to, and the development of the laser turns to improve the beam quality. Diffusion-cooled slab CO2 laser near the diffraction limit has good beam quality and has been widely used, especially in the field of laser cutting, which is favored by many enterprises.
At the beginning of 2 1 century, another new type of laser-semiconductor laser appeared. Compared with the traditional high-power CO2 and YAG solid-state lasers, semiconductor lasers have obvious technical advantages, such as small size, light weight, high efficiency, low energy consumption, long service life and high metal absorption of semiconductor lasers. With the continuous development of semiconductor laser technology, other solid-state lasers based on semiconductor lasers, such as fiber lasers, semiconductor pumped solid-state lasers and sheet lasers, have also developed rapidly. Among them, fiber lasers are developing rapidly, especially rare earth-doped fiber lasers, which should be widely used in optical fiber communication, optical fiber sensing, laser material processing and other fields.
Because of its outstanding characteristics, laser has been rapidly applied to industry, agriculture, precision measurement and detection, communication and information processing, medical treatment, military and other aspects, and has caused revolutionary breakthroughs in many fields. Laser is not only used in communication, night vision, early warning and ranging, but also various laser weapons and laser-guided weapons have been put into practical use.
1. Laser is used as the heat source. The laser beam is small but powerful. If you focus with a lens, you can concentrate energy in a small area and generate huge heat. For example, people can use the concentrated and extremely high energy of laser to process various materials and drill 200 holes in a needle; As a means to stimulate, mutate, cauterize and vaporize organisms, laser has achieved good results in practical applications of medicine and agriculture.
2. Laser ranging. As a ranging light source, laser can measure long distances with high accuracy because of its good directivity and high power.
3. Laser communication. In the field of communication, a light-guiding cable that uses a laser column to transmit signals can carry information equivalent to that carried by 20,000 telephone copper wires.
4. The application of controllable nuclear concentration in air. When the laser irradiates the mixture of deuterium and tritium, it brings them great energy, produces high pressure and high temperature, and promotes the two kinds of nuclei to polymerize into helium and neutrons, and at the same time releases huge radiation energy. Because the laser energy can be controlled, this process is called controlled nuclear fusion.
In the future, with the further development of laser technology, the performance of laser will be further improved and the cost will be further reduced, but its application scope will continue to expand and it will play an increasingly huge role.
Laser pen is a small low-power laser with laser as its pointing purpose, which belongs to general civilian products and is also called laser pen, star pen and so on. It is a multifunctional product: teaching and scientific research units use video equipment as instructions for teaching, academic reports, conferences and other occasions; Instructions used by military units to cooperate with the large-screen command system; Tourism units are used for tour guides to explain; Instructions used by construction and decoration supervision units for construction and decoration acceptance, etc. In some cases, it can also be fixed as a directional tool; It can also be used as a gift.
abstract
There are also many kinds of carbon dioxide lasers that emit by pulse, which are widely used in scientific research and industry. If we compare the energy emitted by each pulse, then the pulsed carbon dioxide laser is the strongest among the pulsed lasers. Here I want to go back to the problem that the laser pioneer town once studied and talk about the generation of millimeter waves. With the development of laser technology, many scientists have tackled this problem: using discharge or powerful carbon dioxide laser as excitation source to excite gas molecules such as fluoromethane and ammonia, and gradually extend and expand the wavelength of the emitted laser. At first, it reached tens of microns, and later it reached hundreds of microns, which is submillimeter wave. From the mid-1960s to the mid-1970s, with the development of microwave technology, scientists produced millimeter waves according to the principles and methods of laser. In this way, the gap between light wave and microwave is filled by the new infrared laser that is constantly discovered.
Scientists have found that millimeter wave has great practical value: the atmospheric absorption rate is small, and it has little influence on its propagation, so it can be used as a new atmospheric communication tool.
Another special and novel laser can be called "chameleon" figuratively. It is not a dragon, but it does change color; As long as you turn the knob on the laser, you can get red, orange, yellow, green, blue, indigo and purple lasers.
Do dyes have anything to do with lasers? Not bad at all. The working substance of this laser is really dyes, such as cyanine, rhodamine and coumarin. Scientists have not yet figured out the molecular energy levels and atomic structures of these dyes, only knowing that they are different from gas atoms and ions of gas working fluids. The laser wavelength produced by gas is certain, while the laser wavelength produced by dye has a wide range, or many colors. Optical elements called gratings are installed in the optical resonator of dye lasers. Through it, you can choose the color of the laser according to your own needs, just like listening to different frequencies on the radio.
Future prospects
The excitation source of dye laser is optical pump, which can use pulsed xenon lamp or laser emitted by nitrogen molecular laser. It can be said that it is one of the characteristics of dye laser to use one color laser as optical pump and produce other colors of laser as a result.
This kind of laser can change the wavelength of laser at any time as needed, which is mainly used for spectral research; Many substances will selectively absorb certain wavelengths of light, thus producing * * * vibration phenomenon. Scientists use these phenomena to analyze matter and understand its structure. These lasers are also used to generate new lasers and study some strange optical and spectral phenomena.
Accident-prone
When using a laser cutting machine, the laser emission of the laser may cause the following accidents: (1) The laser emission touches flammable materials, causing a fire. As we all know, the power of laser generator is very high, especially for high-power laser cutting machine, the laser temperature is very high. There is a great possibility of fire when the laser comes out and touches flammable materials. (2) Harmful gas may be generated when the machine is running. For example, when cutting with oxygen, it will react with the cutting material to produce unknown chemicals or particles and other impurities. After being absorbed by the human body, it may cause allergic reaction or respiratory discomfort such as lungs. Protective measures should be taken during operation. (3) Direct laser beam is harmful to human body. The harm of laser to human body mainly includes the harm to eyes and skin. Among the injuries caused by laser, the damage of the body to the eyes is the most serious. The damage to the eyes is permanent. So you must pay attention to protect your eyes when you do your homework. Therefore, the cutting environment should prohibit flammable objects from approaching the machine and maintain ventilation, and the workplace should also be equipped with fire extinguishers. Staff should take self-protection measures when doing their homework.
future
The fiber laser can output laser in the band of 800 nm-2 100 nm, and the maximum power reaches the order of 10000 watts. Its application has also expanded from optical communication to laser processing, laser marking, image display, bioengineering, medical care and other fields. The future development trend of fiber laser will be reflected in the following aspects:
(1) Improving the performance of fiber laser itself: How to improve the output power and conversion efficiency, optimize the beam quality, shorten the gain fiber length, improve the system stability and make it more compact will be the focus of future research in the field of fiber laser.
(2) Development of new fiber lasers: In the time domain, ultrashort pulse mode-locked fiber lasers with smaller duty cycle have always been a hot spot in the laser field, and high-power femtosecond pulse fiber lasers have always been a long-term goal. The breakthrough in this field can not only provide an ideal light source for optical communication time division multiplexing (OTDM), but also effectively promote the development of related industries such as laser processing, laser marking and laser encryption. In frequency domain, tunable fiber laser with broadband output will become a research hotspot. A nonlinear fiber laser with zirconium, barium, lanthanum, aluminum and neodymium as laser medium has attracted people's attention. The laser has a wide bandwidth and low loss, and can realize wavelength up-conversion in several bands. It is praised by experts as the next generation communication material. If it can be produced on a large scale, it will generate billions of dollars in the fields of laser printing and large-screen display. It can be predicted that with the improvement of related technologies, fiber lasers will develop in a wider field and may become a new generation of light sources to replace solid-state lasers and semiconductor lasers, forming a new industry.