What are the different types of lasers?
This article mainly introduces the different types of lasers and their applications and characteristics.
1. Gas laser
1.1 He-Ne Laser
He-Ne laser: a typical noble gas atom laser, which outputs continuous light, with spectral lines of 632.8nm (the most commonly used), 1015nm, 3390nm, and recently extended to short wavelengths. The maximum output power of this kind of laser can reach 1W, but the beam quality is very good. It is mainly used in precision measurement, detection, collimation, guidance, underwater lighting, information processing, medical treatment and optical research.
1.2 Ar ion laser
Ar ion laser: a typical inert gas ion laser, which uses the ionization and excitation of argon atoms in the gas discharge test tube, and realizes the number inversion between the ion excited state energy levels to generate laser light. The laser spectral lines it emits are in the visible light and ultraviolet regions. In the visible light region, it is the device with the highest output continuous power, and the highest commercialized one is 30-50W. Its energy conversion rate can reach up to 0.6%, the frequency stability is 3E-11, the life span exceeds 1000h, the spectrum is in the blue-green band (488/514.5), and the power is large. It is mainly used for Raman spectroscopy, pump dye laser, holography , nonlinear optics and other research fields, as well as medical diagnosis, printing color separation, metrology material processing and information processing.
1.3 CO2 Lasers
CO2 Lasers with a wavelength of 9~12um (typical wavelength of 10.6um) have many advantages such as high efficiency, good beam quality, large power range (several watts to tens of thousands of watts), both continuous and pulsed. The most important and most widely used type of gas lasers. Mainly used in material processing, scientific research, detection of national defense and so on. Commonly used forms are: sealed-off longitudinal electro-excited carbon dioxide laser, TEA carbon dioxide laser, axial fast-flow high-power carbon dioxide laser, and cross-flow high-power carbon dioxide laser.
1.4 N2 Molecular Laser
N2 molecular laser: gas laser, output ultraviolet light, the peak power can reach tens of megawatts, the pulse width is less than 10ns, and the repetition frequency is tens to kilohertz. It can be used as a pump source for tunable fuel lasers, and can also be used for Fluorescence analysis, detection of pollution, etc.
1.5 Excimer Laser
Excimer laser: a type of gas laser device with excimer as the working substance. Electron beam (energy greater than 200 keV) or transverse rapid pulse discharge is commonly used to achieve excitation. When the unstable molecular bonds of the excited state excimer are broken and dissociated into ground state atoms, the energy of the excited state is released in the form of laser radiation.
The excimer laser material has the repulsion of the low energy state, which can be effectively evacuated, so there is no low state absorption and energy loss, the population inversion is easy, the gain is large, the conversion efficiency is high, the repetition rate is high, and the radiation wavelength is short. It oscillates in the ultraviolet and vacuum ultraviolet (a few extend to visible light) region with a wide tuning range. It can be used in separation of isotopes, ultraviolet photochemistry, laser spectroscopy, rapid photography, high-resolution holography, laser weapons, research on the structure of matter, optical communication, remote sensing, integrated optics, nonlinear optics, agriculture, medicine, biology, and pumping. Tuned dye lasers have been widely used, and are expected to be developed into laser devices for nuclear fusion.
2. Solid-state Laser
2.1 YAG Laser
YAG Laser can be divided into: Nd-YAG crystal, Ce-Nd-YAG crystal, Yb-YAG crystal, Ho-YAG crystal, Er-YAG crystal.
Solid-state Laser, 1064nm, Nd-YAG laser crystal with the most excellent comprehensive performance at present, the maximum output power of continuous laser is 1000W, which is widely used in military, industrial and medical industries.
If the continuous operation is used, the multi-mode output of 400W can be obtained by using one-stage oscillation. If the laser output is at the 100-watt level, a single lamp and a single rod are used, and a double lamp and a single rod structure is used for more than 200W. The Nd-YAG laser is not only suitable for continuous, but also has excellent performance at high repetition frequency. The repetition frequency can reach 100~200 times/s, and the maximum average power can be 400w. Multi-stage series connection is used to achieve high power output. At present, the average power can reach up to 600~800 watts, the repetition frequency can reach 80~200 times/s, and the single pulse energy can reach 80J.
2.1.2 Ce-Nd-YAG Laser
Ce-Nd-YAG is formed by adding Ce ions on the basis of Nd-YAG crystal. The use of Ce ions can produce good absorption of photon energy in the ultraviolet spectral region, and transfer the energy to Nd ions in a non-radiative transition manner, thereby increasing the utilization of the spectrum, so the efficiency is high, the threshold is low, and the repetition frequency characteristics are good.
Yb3+ is doped into a YAG matrix to form a laser crystal that generates a 1.03um near-infrared laser. It belongs to the same matrix as Nd-YAG, but the growth process is different due to different doping. Due to its high quantum efficiency, simple crystal spectrum, no excited state absorption and upconversion, and no fluorescence concentration quenching, Yb-YAG has a high doping concentration, a longer fluorescence lifetime, and a much wider absorption band bandwidth than Nd-YAG. , which can be effectively coupled to the pump wavelength of the diode. Under the same input power, the pumping heat of Yb-YAG is only 1/4 of that of Nd-YAG. Moreover, YAG matrix has the best comprehensive properties of physicochemical properties, so Yb-YAG has become one of the most attractive solid-state laser media. A major direction for the development of high-efficiency, high-power solid-state lasers.
2.1.4 Ho-YAG Laser
Ho-YAG Laser produces eye-safe 2097nm and 2091nm lasers, mainly for optical communication, radar and medical applications. Ho-YAG lasers have strict requirements on cooling and dryness, and water cooling is controlled below 10 degrees Celsius. The drying unit must be free from the influence of water vapour. In the range of the safe band for the human eye, due to the large water absorption, the penetration depth is very shallow, which greatly reduces the possibility of accidental damage to the human body, especially to the eyes.
It outputs a wavelength of 2.9um, which can be absorbed by water, and is mainly used in medicine. The crystal mainly absorbs visible light and ultraviolet light, so the materials of the optical cavity reflector are mostly aluminum and silver with high reflection. At present, the maximum output power of Er-YAG laser can reach 3W, and the maximum pulse output can reach 5J. It is the most efficient long-wavelength solid-state laser with the largest output power so far. The absorption of 2940nm by the human body is ten times that of 10640nm, so laser surgery and vascular surgery have great application potential.
2.2 Ruby Laser
Ruby can only achieve continuous output at low temperature, and the threshold is very high, so so far no continuous output ruby laser that works at room temperature has been built. Suitable for single-shot or low-repetition pulsed lasers. The single pulse energy can reach 1~20J, the repetition frequency is 5~10, and the single pulse energy can reach about 1J.
2.3 Rubidium Glass Laser
Rubidium glass is also difficult to operate at room temperature. Suitable for single-shot or low-repetition pulsed lasers. The repetition frequency is limited to 5 times/s, and the energy of a single pulse can reach 10~80J.
3. Semiconductor Diode Laser
A semiconductor Diode Laser is a device that produces stimulated emission with a certain semiconductor material as the working substance. Its working principle is that, through a certain excitation method, between the energy band (conduction band and valence band) of the semiconductor substance, or between the energy band of the semiconductor substance and the impurity (acceptor or donor) energy level, a non-equilibrium load is realized. The particle number inversion of the streamer occurs when a large number of electrons and holes in the state of particle number inversion recombine, and stimulated emission occurs.
The emission wavelength varies with the band gap.
There are three main excitation modes of semiconductor lasers: electric injection type, optical pump type and high-energy electron beam excitation type.
Electric injection semiconductor lasers are generally semiconductor junction diodes made of materials such as GaAS (gallium arsenide), InAS (indium arsenide), and Insb (indium antimonide), which are excited by injecting current along the forward bias voltage. The junction plane region produces stimulated emission.
Optically pumped semiconductor lasers generally use N-type or P-type semiconductor single crystals (such as GaAS, InAs, InSb, etc.) as the working substance, and use the laser light emitted by other lasers as the optical pump excitation.
High-energy electron beam-excited semiconductor lasers generally use N-type or P-type semiconductor single crystals (such as PbS, CdS, ZhO, etc.) as the working material, and are excited by injecting high-energy electron beams from the outside.
At present, the most commonly used is the electric injection GaAs diode laser with double heterostructure, usually 635 red light; Indium Gallium Nitride (InGaN)
Diode lasers, commonly 532 green and 405 blue. The laser light emitted by a diode laser can be described as a Gaussian beam, which is characterized by an elongated emitter with different emission angles in the horizontal and vertical directions. Usually only a few degrees horizontally, and up to 40 degrees vertically. In most optical coupling techniques, the horizontal angle is ignored, and the vertical angle is used as the divergence angle of the laser.
Mainly used in electronic information. Optical fiber communication, optical sensing, optical disc, laser printing, barcode scanning, integrated optics.
400~780nm applications are used for bar scanning, inspection, optical storage, laser printing, etc.
790~1020nm is used in barcode scanning, laser printing, optical storage and other fields. In recent years, high-power semiconductor lasers have made great progress, and the continuous output power can reach 1~20w.
1300 and 1550 are respectively in the zero dispersion and lowest loss windows of silicon fiber, and the corresponding semiconductors are mainly used for long-distance large-capacity trunk optical communication.Between 1300 and 1550, the output power of 1480 can reach 50~100mw in recent years.
4. Dye Laser
Its outstanding advantage is that the output wavelength is tunable, it can not only obtain a tunable narrow-band high-power laser within the 0.3~1.3um spectrum, but also obtain tunable coherent light from ultraviolet to mid-infrared through frequency mixing technology, so Currently mainly used for spectroscopy research.
5. Fiber Laser
Fiber lasers have a wide range of applications, including laser fiber optic communications, laser space telecommunication, industrial shipbuilding, automobile manufacturing, laser engraving, laser marking, laser cutting, printing rolls, metal and non-metal drilling/cutting/welding, military defense and security, Medical equipment and equipment, large-scale infrastructure, etc.
The advantages of miniaturization and intensification brought by the low manufacturing cost, mature technology and the flexibility of the optical fiber; the glass optical fiber does not require strict phase matching like the crystal for the incident pump light, which is due to the glass matrix Stark The non-uniform broadening caused by splitting causes the absorption band to be wider; the glass material has a very low volume area ratio, fast heat dissipation and low loss, so the up-conversion efficiency is high and the laser threshold is low;
The output laser has many wavelengths: this is because the energy level of rare earth ions is very rich and there are many kinds of rare earth ions; Tunability: because of the wide energy level of rare earth ions and the wide fluorescence spectrum of glass fiber.
Since there is no optical lens in the resonant cavity of the fiber laser, it has the advantages of adjustment-free, maintenance-free and high stability, which is unmatched by traditional lasers.
The fiber export makes the laser easily competent for various three-dimensional arbitrary space processing applications, which makes the design of the mechanical system very simple.
Competent in harsh working environments, it has a high tolerance for dust, shock, shock, humidity and temperature. No need for thermoelectric cooling and water cooling, just simple air cooling.
High electro-optical efficiency: The comprehensive electro-optical efficiency is as high as 20% or more, which greatly saves power consumption during work and saves operating costs. High-power, currently commercial fiber lasers can reach up to six kilowatts.
6. Free Electron Laser
The output laser wavelength is related to the energy of the electrons: therefore, changing the accelerating voltage of the electron beam can change the laser wavelength, which is called voltage tuning, which has a wide tuning range and can operate at any wavelength in principle.
Under the experimental conditions of existing electron guns and accelerators, continuously tuned coherent radiation in the range from millimeter wave to optical frequency band can be obtained. The output power of the free electron laser is related to the energy, current density and magnetic induction intensity of the electron beam. It is expected to become a high-average power, high-efficiency (theoretical limit up to 40%), high-resolution and stable power and frequency output. Laser devices can avoid some process troubles (such as scarcity of laser working materials, toxic or corrosive metals and glass), and basically there is no service life problem.
Free electron lasers have opened up a new way for laser research in the four main directions of short wavelength, high power, high efficiency and adjustable wavelength. It is expected to be used for condensed matter physics, material characteristics, laser weapons. , laser anti-missile, radar, laser fusion, plasma diagnostics, surface properties, nonlinear and transient phenomena research, in the fields of communication, laser thrusters, spectroscopy, laser molecular chemistry, photochemistry, isotope separation, remote sensing, etc. The application prospect is also very impressive.
The airborne laser weapon system of the United States uses the high-energy chemical iodine oxygen free electron laser (COIL).
7. Diode-pumped Solid-state Laser
Diode Lasers and Diode-pumped Solid-state Lasers have now become the mainstream of solid-state laser development. They have high combined conversion efficiency, good stability and high reliability. They are the only maintenance-free laser systems so far, with high output quality, small size and compact structure Features. Key technologies of diode-pumped solid-state lasers: optical coupling technology, pumping technology, cooling technology and power supply technology. The output power of this laser can vary widely, from tens of watts to several kilowatts, and the largest commercial one on the market can reach 6000w.
8. Solid UV Laser
There are currently two main ways:
(1) Direct frequency doubling of LD output to obtain ultraviolet laser. Ultraviolet is obtained by double frequency doubling infrared, which has high light-to-light conversion efficiency, but requires LD not only to have high output, but also to achieve single-frequency operation.
(2) LD-pumped, nonlinear optical frequency-converted ultraviolet laser. The method mainly utilizes that the emission band of the laser diode is in good agreement with the absorption band of the rubidium ion, thereby reducing the inner product of the energy, thereby reducing the thermal lens effect, improving the beam quality, and obtaining high pumping efficiency.