Laser

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laser is a device that emits light through an optical amplification process based on the emission of stimulated electromagnetic radiation. The term "laser" originates as an acronym for "light amplification by emitted radiation emission ". The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical works by Charles Hard Townes and Arthur Leonard Schawlow.

Lasers differ from other light sources that emit light coherently , spatially and temporally. Spatial coherence allows the laser to be focused to a narrow area, enabling applications such as laser cutting and lithography. Spatial coherence also allows the laser beam to remain narrow at a great distance (collimation), enabling applications such as laser pointers. Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum, that is, they can emit a single color of light. Temporal coherence can be used to produce light pulses as short as femtoseconds.

Among their many applications, lasers are used in optical disk drives, laser printers, and barcode scanners; DNA sequencing instruments, optical fibers and free space optical communications; laser surgery and skin care; cut and weld; military and law enforcement devices to mark targets and measure reach and speed; and display laser lighting in entertainment.

Video Laser

Fundamentals

The laser is distinguished from other light sources by its coherence. Spatial coherence is usually expressed through output into narrow beam, which is a finite diffraction. Laser rays can be focused to a very small point, reaching very high radiation, or they can have very low divergences to concentrate their power at great distances.

The temporal (or elongated) coherence implies polarized waves at a single frequency whose phases are correlated over a relatively large distance (coherence length) along the beam. Rays generated by other thermal or incoherent light sources have instant amplitude and phase varying randomly to time and position, thus having short coherence lengths.

Lasers are characterized according to their wavelengths in a vacuum. Most "single wavelength" lasers actually produce radiation in some modes having slightly different frequencies (wavelengths), often not in a single polarization. Although temporal coherence implies monochromaticity, there are lasers that emit a broad spectrum of light or emit different wavelengths of light simultaneously. There are some lasers that are not single spatial modes and consequently have a beam of light that deviates more than is required by the diffraction limit. However, all such devices are classified as "lasers" based on their method of producing light, that is, stimulated emissions. Lasers are used in applications where the required spatial or temporal coherence light can not be produced using simpler technology.

Terminology

The word laser begins as an acronym for "amplification of light by the emission of radiation that is stimulated". In this use, the term "light" includes electromagnetic radiation of any frequency, not only visible light, hence the term infrared laser, ultraviolet laser, laser X-ray , gamma-laser rays , and so on. Because microwave laser predecessors, maser, developed first, such devices operate on microwaves and radio frequencies referred to as "masers" rather than "microwave lasers" or "laser radios". In the early technical literature, especially at Bell Telephone Laboratories, the laser was called optical maser ; this term is now outdated.

Lasers that produce light by themselves are technically optical oscillators rather than optical amplifiers as suggested by acronyms. It has been funny to note that the abbreviation LOSER, for "light oscillations by stimulated emission of radiation", would be more correct. With the widespread use of the original acronym as a common noun, the optical amplifier has been referred to as a "laser amplifier", regardless of the redundancy seen in the designation.

The back-converted verb to lase is often used in the field, which means "generating laser light", especially in reference to the laser gain medium; when the laser is operating it says "amplifier." Further use of the words laser and maser in a broad sense, not referring to laser or device technology, can be seen in uses such as astrophysical maser > and atomic lasers .

Maps Laser

Design

The laser consists of a gain medium, a mechanism for energizing, and something to provide optical feedback. The media gain is a material with properties that allow it to amplify light by means of stimulated emission. Certain light wavelengths through the gain medium are amplified (power increase).

For strengthening media to amplify light, it needs to be supplied with energy in a process called pumping. Energy is usually given as an electric current or as a light at different wavelengths. Pump lamps can be provided by flash or by other lasers.

The most common type of laser uses feedback from optical cavities - a pair of mirrors at either end of the gain medium. Light bounces back and forth between the mirrors, passes through the gain medium and is amplified each time. Usually one of two mirrors, output coupler, partially transparent. Some light passes through this mirror. Depending on the design of the cavity (whether the mirror is flat or curved), light coming out of the laser can spread or form a narrow beam. In analogous to the electronic oscillator, this device is sometimes called the laser oscillator .

Most practical lasers contain additional elements that affect the properties of emitted light, such as polarization, wavelength, and light form.

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Laser physics

Electrons and how they interact with an important electromagnetic field in our understanding of chemistry and physics.

Stimulate emissions

In the classical view, the energy of electrons orbiting the nuclei of atoms is greater to orbit further from the atomic nucleus. However, the effects of quantum mechanics force electrons to take discrete positions in orbitals. Thus, the electrons are found in the atomic specific energy levels, two of which are shown below:

When an electron absorbs energy from either light (photons) or heat (phonons), the electrons receive quantum energy. But transitions are only allowed between discrete energy levels like the two shown above. This causes the emission lines and absorption path.

When an electron is excited from a lower to a higher energy level, it will not stay that way forever. An electron in an excited state can decay into an unfilled lower energy state, corresponding to a constant time constant that characterizes the transition. When an electron decays without external influence, it emits a photon, called "spontaneous emission". Phases associated with emitted photons are random. Materials with many atoms in such excited states can produce very spatially limited radiation (centered around one wavelength of light), but individual photons do not have a common phase relationship and will radiate in random directions. It is a fluorescence and heat emission mechanism.

External electromagnetic fields at frequencies associated with transitions can affect the atomic quantum mechanics status. When an electron in an atom makes a transition between two stationary states (none showing the dipole field), it enters a transition state that does have a dipole field, and which acts like a small electric dipole, and the dipole oscillates at its characteristic frequency. In response to external electric fields at these frequencies, the probability of atoms entering this transition state is greatly increased. Thus, the transition rate between two stationary states increases beyond that due to spontaneous emissions. Such a transition to a higher state is called absorption, and destroys incident photons (the energy of photons goes into powering the increased energy from the higher state). The transition from higher to lower energy states, however, produces additional photons; this is a emulated emission process.

Obtain medium and cavity

The gain media is fed into an excited state by an external energy source. In most lasers, this medium consists of atomic populations that have been attracted to such a state by using an outside light source, or an electric field that supplies energy to the atoms to absorb and convert to their excited state.

The media gain of a laser is usually a controlled purity material, size, concentration, and shape, which amplifies the rays by the stimulated emission process described above. This material may be: gaseous, liquid, solid, or plasma. The media gain absorbs the pump energy, which raises several electrons to a high energy quantum state ("excited"). Particles can interact with light by absorbing or emitting photons. Emissions may be spontaneous or aroused. In the latter case, the photon is transmitted in the same direction as the passing light. When the number of particles in an excited state exceeds the number of particles in some low energy state, population inversion is achieved and the amount of emission is stimulated because the passing light is greater than the amount of absorption. Therefore, light is reinforced. By itself, this makes the optical amplifier. When the optical amplifier is placed inside the resonant optical cavity, one obtains a laser oscillator.

In some situations it is possible to obtain an amplifier with only one EM radiation pass through the gain medium, and this produces a laser beam without requiring a resonant or reflective cavity (see eg nitrogen laser). Thus, reflections in the resonance cavity are usually required for lasers, but not absolutely necessary.

Optical resonators are sometimes referred to as "optical cavities", but this is a mistake: the laser uses an open resonator as opposed to a literal cavity that will be used at microwave frequencies in the maser. The resonator usually consists of two mirrors in which coherent light travels in both directions, reflecting itself back so that the average photon will pass through the gain medium repeatedly before being emitted from the output aperture or lost to diffraction or absorption. If the amplification (amplification) in the medium is greater than the resonator losses, then the strength of the recirculating light may increase exponentially. But each stimulated emission event returns the atom from the excited state to the ground state, reducing the acquisition of the medium. With increasing ray power, net gain (gain minus loss) reduces to unity and the gain medium is said to be saturated. In a continuous wave laser (CW), the balance of the pump power to gain saturation and cavity loss produces a laser power balance value in the cavity; This equilibrium determines the laser operating point. If the applied pump power is too small, the gain will not be sufficient to overcome the loss of the cavity, and the laser beam will not be produced. The minimum pump power required to start a laser action is called lasing threshold . The gain media will amplify every photon passing through it, regardless of its direction; but only photons in spatial mode supported by the resonator will pass more than once through the medium and receive substantial amplification.

Light emitting

The light generated by the stimulated emission is very similar to the input signal in terms of wavelength, phase, and polarization. It provides its characteristic coherence laser beam, and allows it to maintain the uniform polarization and often monochromaticity set by the optical cavity design.

The rays in the cavities and laser beam output, while traveling in free space (or homogeneous medium) rather than waveguide (as in fiber optic lasers), can be estimated as Gaussian rays in most lasers; the beam indicates a minimum difference for a given diameter. However some high power lasers may be multimode, with transverse modes often approximated using the Hermite-Gaussian or Laguerre-Gaussian function. It has been shown that unstable laser resonators (not used in most lasers) produce fractal beams. Near the "waist" beam (or focus area) is very collimated : the wavefront is planar, normal in the direction of propagation, without the difference of light at that point. However, because of the diffraction, it can only stay true within the Rayleigh range. The light from a single gaussian beam (laser gamma-beam) ultimately deviates at an angle that varies inversely with the beam diameter, as required by the diffraction theory. Thus, the "pencil beam" produced directly by ordinary helium-neon lasers will spread to a size perhaps 500 kilometers when it shines on the Moon (from Earth's distance). On the other hand, the light from a semiconductor laser is usually out of a small crystal with a large divergence: up to 50 °. But even different rays can be transformed into a similar collimation beam using a lens system, as always included, for example, in a laser pointer whose light comes from a laser diode. That may be due to the light from a single spatial mode. The unique nature of this laser beam, spatial coherence, can not be replicated using standard light sources (except by removing most of the light) as can be appreciated by comparing rays from flashlights (torches) or spotlights to almost any laser.

Quantum vs classic emission process

The mechanism of generating radiation in the laser depends on the stimulated emission, in which energy is extracted from transitions in atoms or molecules. This is a quantum phenomenon discovered by Einstein that obtains a relationship between coefficient A which describes spontaneous emission and coefficient B applicable to absorption and stimulated emission. However, in the case of free electron lasers, the level of atomic energy is not involved; it appears that the operation of this somewhat exotic tool can be explained without reference to quantum mechanics.

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Continuous and pulsed operation mode

Lasers can be classified to operate in continuous or pulsed mode, depending on whether the power output is substantially continuous over time or whether the output takes the form of a pulse of light on a time scale or another. Of course even lasers whose outputs are usually continuous can be intentionally turned on and off at a certain level to create a pulse of light. When the modulation level is on a time scale much slower than the life span of the cavity and the time period in which energy can be stored in a propulsion or pumping mechanism, it is still classified as a "modulated" or "pulsed" continuous wave laser. Most laser diodes used in communication systems fall into that category.

Continuous wave operation

Some laser applications rely on rays whose output power is constant over time. Such lasers are known as continuous wave ( CW ). Many types of lasers can be made to operate in continuous wave mode to meet such applications. Many of these lasers actually lase in some longitudinal modes at the same time, and beats between slightly different optical frequencies of the oscillations will actually produce amplitude variations on a shorter time scale than round-trip time (as opposed to the frequency range between modes), usually a few nanoseconds or less. In many cases, this laser is still called a "continuous wave" because its output power is stable when averaged over a longer period of time, with very high frequency power variations that have little or no impact in the intended application. (This term, however, is not applied to locked-mode lasers, where intention is to create very short pulses at an alternating time rate).

For continuous wave operation, it is necessary for the population inversion of the gain medium to be continuously replenished by a stable pump source. In some lasing media this is not possible. In some other lasers will require pumping the laser at a very high continuous power level that would be impractical or destroy the laser by generating excessive heat. Such lasers can not be run in CW mode.

Pulsed Operation

Pulsed laser operation refers to lasers that are not classified as continuous waves, so that optical power appears in multiple pulses of duration at multiple repeatability levels. It covers various technologies that address a number of different motivations. Some lasers pulsate just because they can not be run in continuous mode.

In other cases, the application requires the production of pulses to have as much energy as possible. Since the pulse energy is equal to the average power divided by the repetition rate, this goal can sometimes be met by decreasing the pulse rate so that more energy can be built up between the pulses. In laser ablation, for example, small volumes of material on the surface of the workpiece can be evaporated if heated in a very short period of time, while supplying energy gradually will allow heat to be absorbed into most pieces, never reaching a sufficiently high temperature at some point.

Other applications depend on the strength of the peak pulse (not energy in the pulse), especially to get nonlinear optical effects. For a given pulse energy, this requires creating a pulse with a duration that might use a technique such as Q-switching.

The optical bandwidth of the pulse can not be more narrow than the opposite of the pulse width. In the case of very short pulses, which means the amplifier is more than adequate bandwidth, very much at odds with the very narrow bandwidth typical of a CW laser. Reinforcing media in some dye lasers and vibronic solid-state lasers result in optical advantages over a wide bandwidth, making possible lasers that can produce light pulses as short as several femtoseconds (10 ^-15 s).

Q-switching

In Q-switched lasers, population inversions are allowed to build by including losses in a resonator that exceeds the medium's gain; this can also be described as a reduction of the quality factor or 'Q' of the cavity. Then, once the pump energy stored in the laser medium has approached the maximum possible level, the introduced loss mechanism (often an electro-or acousto-optical element) is quickly removed (or occurring on its own in the passive device), allowing the amplifier to start with quickly gain energy stored in the media gain. This produces a short pulse that combines that energy, and thus high peak power.

Lock mode

A locked-mode laser is able to emit very short pulses on the order of tens of picoseconds to less than 10 femtoseconds. These pulses will be repeated at the return time, ie the time it takes the light to complete a spin between a mirror consisting of a resonator. Because of the Fourier limit (also known as time-energy uncertainty), such short-term pulses have spectrum scattered over a considerable bandwidth. Thus, such gain media must have a sufficiently large gain bandwidth to amplify that frequency. Examples of suitable materials are titanium-doped, artificial sapphire (Ti: sapphire) which has very wide bandwidth gain and thus can produce pulses of only a few femtoseconds duration.

The locked-mode laser is the most versatile tool for researching processes that occur on very short time scales (known as femtosecond physics, femtosecond chemistry and ultrafast science), to maximize nonlinear effects in optical materials (eg in second-harmonic, parametric down-conversion, optical parametric oscillators and the like). Due to its large peak power and ability to produce stable phase trains from ultra-fast laser pulses, ultra-locking laser modes support precision metrology and spectroscopy applications.

Pulsed pumping

Another method to achieve pulsed laser operation is to pump the laser material with its own pulsed source, either via electronic charging in case of flash, or other pulsed laser. Historically pulsed pumping is used with laser dyes in which the life spans of the dye molecule population that are too short is so short that it takes high energy, fast pumps. The way to solve this problem is to charge a large capacitor which then switches to discharge via flashlamps, producing an intense flash. Pulverization pumping is also required for three-level lasers where lower energy levels quickly become very dense, preventing further uplift until they are relaxed to ground state. These lasers, such as excimer lasers and copper steam lasers, can never be operated in CW mode.

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History

Foundation

In 1917, Albert Einstein founded the theoretical foundation for lasers and masers on the paper Zur Quantentheorie der Strahlung (In Quantum Radiation Theory) through the re-derivation of the Max Planck radiation law, conceptually based on the probability coefficient (Einstein coefficient) for absorption, spontaneous emission, and emission triggered electromagnetic radiation. In 1928, Rudolf W. Ladenburg asserted the phenomenon of stimulated emission and negative absorption. In 1939, Valentin A. Fabrikant foresees the use of stimulated emission to amplify the "short" wave. In 1947, Willis E. Lamb and R. C. Retherford found emission stimulated in the hydrogen spectrum and influenced the first demonstration of stimulated emission. In 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed an optical pumping method, confirmed experimentally, two years later, by Brossel, Kastler, and Winter.

Maser

In 1951, Joseph Weber filed a paper on the use of stimulated emission to make a microwave amplifier to the Research Conference of the Tube Engineer Convention June 1952 in Ottawa, Ontario, Canada. After this presentation, RCA asked Weber to give a seminar on this idea, and Charles Hard Townes asked him for a copy of the paper.

In 1953, Charles Hard Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifiers, devices that operate on the same principle as lasers, but reinforce microwave radiation rather than infrared or visible radiation. Maser Townes is unable to produce sustainable output. Meanwhile, in the Soviet Union, Nikolay Basov and Aleksandr Prokhorov independently worked on quantum oscillators and solved the problem of continuous-output systems using more than two energy levels. This media gain can release stimulated emissions between excited states and lower excited states, not the ground state, which facilitates the maintenance of the population inversion. In 1955, Prokhorov and Basov suggested optical pumping of multi-level systems as a method of obtaining population inversion, then the main method of laser pumping.

Townes reports that some prominent physicists - among them Niels Bohr, John von Neumann, and Llewellyn Thomas - argue that maser violates Heisenberg's uncertainty principle and therefore can not function. Others like Isidor Rabi and Polykarp Kusch expect that it is impractical and not worth the effort. In 1964 Charles H. Townes, Nikolay Basov, and Aleksandr Prokhorov shared the Nobel Prize in Physics, "for fundamental work in the field of quantum electronics, which has led to the development of oscillators and amplifiers based on laser-maser principles".

Laser

In 1957, Charles Hard Townes and Arthur Leonard Schawlow, then at Bell Labs, began serious research on infrared lasers. As ideas develop, they leave infrared radiation to concentrate on visible light. The concept originally called "optical maser". In 1958, Bell Labs filed a patent application for the proposed optical maser; and Schawlow and Townes submitted their theoretical calculation texts to the Physical Review, published that year at Volume 112, Issue No. 98. 6.

At the same time, at Columbia University, graduate student Gordon Gould is working on a doctoral thesis on the energy level of a vibrant thallium. When Gould and Townes meet, they talk about emission of radiation, as a common subject; thereafter, in November 1957, Gould recorded his ideas for "lasers", including using open resonators (then an important component of laser devices). In addition, in 1958, Prokhorov independently proposed the use of open resonators, the first appearance published (in the Soviet Union) of this idea. Elsewhere, in the US, Schawlow and Townes have approved an open laser laser resonator design - apparently unaware of the unpublished publications of Prokhorov and Gould laser work.

At a conference in 1959, Gordon Gould published the term LASER in the paper The LASER, Light Amplification by Stimulated Emission of Radiation. Gould's linguistic intention uses the word particle "-aser" as a suffix - to accurately represent the light spectrum emitted by the LASER device; thus x-rays: xaser , ultraviolet: uvaser , and so on; no one sets itself as a separate term, although "raser" is briefly popular for showing radio frequency transmitting devices.

Gould notes include possible applications for lasers, such as spectrometry, interferometry, radar, and nuclear fusion. He continued to develop the idea, and applied for a patent in April 1959. The US Patent Office rejected his application, and granted the patent to Bell Labs, in 1960. It provoked a twenty-eight-year lawsuit, which featured prestige and scientific money at stake. Gould won his first small patent in 1977, but only in 1987 he won a significant first patent lawsuit, when a Federal judge ordered the US Patent Office to issue a patent to Gould to pump laser and laser gas disposal devices. The question of how to set credit for creating lasers remains unsolved by historians.

On May 16, 1960, Theodore H. Maiman operated the first laser to function at Hughes Research Laboratories, Malibu, California, in front of several research teams, including Townes, at Columbia University, Arthur Schawlow, at Bell Labs, and Gould, Technical Research Group). Maiman functional lasers use synthetic ruby ​​crystals fitted with a solid flashlamp to produce red laser light, at a wavelength of 694 nanometers; However, the device is only capable of performing pulse operations, due to its three-stage pumping design scheme. Later that year, Iranian physicist Ali Javan, and William R. Bennett, and Donald Herriott, built the first gas laser, using helium and fluorescent fluids capable of continuous operation in infrared (US Pat. No. 3,149,290); later, Javan received the Albert Einstein Prize in 1993. Basov and Javan proposed the concept of a semiconductor laser diode. In 1962, Robert N. Hall demonstrated the first laser diode device, made of gallium arsenide and emitted at 850 nm in the near-infrared spectrum spectrum. Later that year, Nick Holonyak, Jr. demonstrating the first semiconductor laser with visible emissions. This first semiconductor laser can only be used in pulsed light operations, and when cooled to liquid nitrogen temperature (77Ã,K). In 1970, Zhores Alferov, at USSR, and Izuo Hayashi and Morton Panish from Bell Telephone Laboratories also independently developed a room temperature, continuous laser diode operation, using heterojunction structures.

Latest innovation

Since the early period of laser history, laser research has resulted in a wide range of enhanced and specialized lasers, optimized for various performance targets, including:

• new wavelength band
• maximum average output power
• maximum peak pulse energy
• maximum peak pulse strength
• minimum output pulse duration
• minimum linewidth
• maximum power efficiency
• minimum cost

and this study continues to this day.

By 2017, researchers at TU Delft demonstrated the Josephson Junction microwave Microwave laser. Because the laser operates in a superconducting regime, it is more stable than other semiconductor-based lasers. This device has potential for applications in quantum computing. In 2017, researchers at TU Munich demonstrated the smallest laser locking mode that is able to emit pairs of phase-locked picosecond laser pulses with repetition frequencies up to 200 GHz.

In 2017, researchers from Physikalisch-Technische Bundesanstalt (PTB), together with US researchers from JILA, a joint institute of the National Institute of Standards and Technology (NIST) and University of Colorado Boulder, set a new world record by developing an erbium fiber laser -doped with linewidth only 10 millihertz.

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The type and principle of operation

For a more complete list of laser types, check out this list of laser types.

Laser gas

After the discovery of the HeNe gas laser, many other gas discharges have been found to strengthen the light coherently. Gas lasers using many different gases have been built and used for many purposes. The helium-neon (HeNe) laser is capable of operating at a number of different wavelengths, but most are engineered for lase at 633 nm; This relatively low but very coherent laser is very common in optical research and educational laboratories. Commercial carbon dioxide (CO ₂ ) lasers can emit hundreds of watts in a single spatial mode that can be concentrated into small dots. This emission is in thermal infrared at 10.6 Ã,Âμm; Such lasers are regularly used in industry for cutting and welding. The CO ₂ laser efficiency is unusually high: over 30%. Argon-ion lasers can operate on a number of ampli fi er transitions between 351 and 528,7Ã, nm. Depending on the optical design of one or more of these transitions can be simultaneous amplifiers; the most commonly used lines are 458 m, 488 nm and 514.5 nm. Transverse gas nitrogen in the gas at atmospheric pressure (TEA) laser is a cheap gas laser, often made by the hobbyist, which produces incoherent UV light at 337.1 nm. Metal ion laser is a gas laser that produces deep ultraviolet waves. Helium-silver (HeAg) 224 nm and 248 nm neon-copper (NeCu) are two examples. Like all low-pressure gas lasers, the media gain of these lasers has fairly narrow oscillation linewidths, less than 3 GHz (0.5 picometers), making them candidates for use in Raman's suppressed spectraphic fluorescence.

Laser chemistry

Chemical lasers are supported by chemical reactions that allow large amounts of energy to be released quickly. These very high power lasers are particularly attractive to the military, but continuous wave laser chemistry at very high power levels, which are streamed by gas, has been developed and has several industrial applications. For example, in a hydrogen fluoride laser (2700-2900m) and a laser deuterium fluoride (3800m) reaction is a combination of hydrogen gas or deuterium with an ethylene burning product in nitrogen trifluoride.

Excimer laser

The excimer laser is a special type of gas laser that is powered by an electric discharge in which the amplifier medium is an excimer, or rather exciplex in the existing design. This is a molecule that can only exist with one atom in an excited electronic state. Once the molecules transfer the excitation energy to the photons, therefore, the atoms are no longer bound to each other and the molecules are destroyed. This drastically reduces the population of lower energy states so it greatly facilitates population inversion. Excimers currently used are all noble gas compounds; the noble gases are chemically inert and can only form compounds while in an excited state. Excimer lasers typically operate at ultraviolet wavelengths with major applications including semiconductor photolithography and LASIK eye surgery. Commonly used excimer molecules include Arf (emission at 193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm), and XeF (351 nm). Molecular fluorine lasers, emitting at 157nm in ultraviolet vacuum are sometimes referred to as excimer lasers, but this seems to be a misnomer because F ₂ is a stable compound.

Solid-state Laser

The solid-state laser uses a crystal or glass rod that "flows" with ions that provide the required energy status. For example, the first laser used was a ruby ​​laser, made of ruby ​​â € <â € <(chromium-doped corundum). Population inversions are actually maintained in dopants. These materials are optically pumped using a wavelength shorter than the wavelength of the amplifier, often from flashtube or from another laser. The use of the term "solid-state" in laser physics is narrower than typical usage. Semiconductor lasers (laser diodes) are usually not called solid-state lasers.

Neodymium is common dopant in a variety of solid state laser crystals, including yttrium orthovanadate (Nd: YVO ₄ ), yttrium lithium fluoride (Nd: YLF) and yttrium aluminum garnet (Nd: YAG). All of these lasers can produce high strength in the infrared spectrum at 1064 nm. They are used for cutting, welding and metal marking and other materials, and also in spectroscopy and for pumping laser dyes. These lasers are also often frequency doubled, tripled or quadrupled to produce 532 nm (green, visible), 355 nm and 266? Nm (UV) beams, respectively. Dual-solidified solid-state diode (DPSS) diodes are used to create bright green laser pointers.

Ytterbium, holmium, thulium, and erbium are other common "dopants" in solid-state lasers. Ytterbium is used in crystals such as Yb: YAG, Yb: KGW, Yb: BOYS, Yb: CaF ₂ , usually operating about 1020-1050Ã, nm. They are potentially very efficient and high powered because of small quantum defects. The very high strength in ultrashort pulses can be achieved by Yb: YAG. Holocaust-doped YAG crystals emit at 2097 nm and form an efficient laser operation at an infrared wavelength highly absorbed by water-bearing tissue. The Ho-YAG is usually operated in pulsed mode, and passes a fiber optic surgical device to coat the joints, remove rotting from teeth, evaporate cancer, and destroy kidneys and gallstones.

Titanium-doped sapphire (Ti: sapphire) produces a highly adjustable infrared laser, commonly used for spectroscopy. It is also famous for use as a locked-mode laser to generate ultrashort pulses from extremely high peak power.

Thermal limitations on solid-state lasers arise from unconverted pump strengths that heat the medium. This heat, when combined with high thermo-optical coefficients (d n /d T ) can cause thermal lenses and reduce quantum efficiency. Diode-pumped thin-disk lasers overcome this problem by having a gain medium that is much thinner than the diameter of the pump beam. This allows a more uniform temperature in the material. The thin disk laser has been shown to produce blocks up to one kilowatt.

Laser fiber

A solid-state laser or laser amplifier in which light is guided due to total internal reflection in a single mode fiber optic fiber laser. Light guides allow very long areas to produce good cooling conditions; fiber has a ratio of surface area to volume that allows efficient cooling. In addition, the properties of waveguiding fibers tend to reduce the thermal distortion of the beams. Ion Erbium and ytterbium are common species that are common in such lasers.

Quite often, the laser fiber is designed as a double-wrapped fiber. This type of fiber consists of fiber core, cladding inside and outer layer. An index of three concentric layers is chosen so that the fiber core acts as a single-mode fiber for laser emissions while the outer cladding acts as a very high multimode core for pump lasers. This allows the pump to propagate large amounts of power into and through the core region in active, while still having a high numerical aperture (NA) to have an easy launch condition.

Light pumps can be used more efficiently by making a fiber laser disk, or a pile of such lasers.

The laser fiber has a fundamental limit in light intensity in the fiber can not be so high that the optical nonlinear induced by local electric field strength can become dominant and prevent laser surgery and/or lead to the destruction of the fiber material. This effect is called photodarkening. In bulk laser materials, refrigeration is not very efficient, and it is difficult to separate photodarkening effects from thermal effects, but experiments in fibers suggest that photodarkening may be associated with the formation of long-life color centers.

Photonic crystal laser

Photonic crystal lasers are laser based on nanostructures that provide the confinement mode and optical structure density (DOS) required for feedback to occur. They are micrometer size and can be adjusted on photonic crystal tape.

Semiconductor laser

Semiconductor lasers are electrically pumped diodes. Recombination of electrons and holes created by the applied current will produce optical gain. Reflections from the ends of crystals form an optical resonator, although the resonator can be external to the semiconductor in some designs.

Commercial laser diodes emit at wavelengths from 375 nm to 3500 nm. Low to medium power laser diodes are used in laser pointers, laser printers and CD/DVD players. Laser diodes are also often used to pump other lasers optically with high efficiency. The industry's highest power laser diode, with power up to 10 kW (70 dBm), is used in industry for cutting and welding. The external semiconductor laser cavity has an active medium of semiconductors in a larger cavity. This device can produce high-power output with good emission quality, narrow-wavelength linear-wave radiation, or ultrashort laser pulses.

In 2012, Nichia and OSRAM develop and produce high power commercial green laser diodes (515/520Ã, nm), which compete with traditional diode-pumped solid-state lasers.

The vertical surface transmitter laser (VCSEL) is a semiconductor laser whose directional direction is perpendicular to the surface of the wafer. VCSEL devices usually have beam output that is more rounded than conventional laser diodes. In 2005, only 850 VCSELs were widely available, with 1,300 nm VCSEL being commercialized, and 1550 nm devices were research fields. VECSEL is VCSEL external cavity. Semiconductor laser quantum cascade laser that has an active transition between the energy sub-band of an electron in a structure containing multiple quantum wells.

The development of silicon lasers is important in the field of optical computing. Silicon is the material of choice for integrated circuits, and electronic and silicon photonic components (such as optical interconnects) can be made on the same chip. Unfortunately, silicon is a binding agent that is difficult to handle, because it has certain properties that block the amplifier. However, recently the team has produced silicon lasers through methods such as fabrication of lasing materials from silicon and other semiconductor materials, such as indium (III) phosphide or gallium (III) arsenide, a material that allows coherent light to be generated from silicon. This is called a hybrid silicone laser. The latest developments also show the use of monolithic monolithic nanowire lasers on silicon for optical interconnects, paving the way for chip-level applications. This nanowire heterostructure laser capable of optical interconnections in silicon is also capable of emitting pairs of phase-locked picosecond pulses with recurrence frequencies up to 200 GHz, allowing for on-chip optical signal processing. Another type is the Raman laser, which utilizes Raman scattering to produce lasers from materials such as silicon.

Amplifiers without maintaining a vibrant medium to population inversion were shown in 1992 in sodium gas and again in 1995 in rubidium gases by various international teams. This is achieved by using an external maser to induce "optical transparency" in the medium by introducing and destructively disrupting the transition of ground electrons between the two paths, allowing the electrons of the soil to absorb any energy has been canceled.

Dye laser

Dye lasers use organic dyes as a gain medium. The wide gain spectrum of available dyes, or mixtures of dyes, allows the laser to be highly palpable, or to produce very short pulses (on the order of several femtoseconds). Although these tunable lasers are primarily known in their liquid form, the researchers have also demonstrated a narrow linewidite tunable emission in a dispersive oscillator configuration that incorporates solid dye gain media. In the most common form of this solid state dye laser use dye-doped polymers as a laser medium.

Free electron laser

The free-electron electrons, or FELs, produce high coherent, widely palpable, high-strength radiation, which now starts in the wavelength of the microwaves through terahertz radiation and infrared to the visible spectrum, to the soft X-rays. They have the widest frequency range of any type of laser. While FEL beams share the same optical properties as other lasers, such as coherent radiation, the FEL operation is very different. Unlike gases, liquids, or solid-state lasers, which depend on the attached atomic or molecular state, the FEL uses relativistic electron beams as a reinforcing medium, hence the term "free electron .

Exotic media

The pursuit of high-energy quantum lasers using the transition between the isomeric state of the atomic nucleus has been the subject of extensive academic research since the early 1970s. Much of this is summarized in three review articles. This research is international, but mainly based in the former Soviet Union and the United States. While many scientists remain optimistic that a breakthrough is imminent, operational gamma ray lasers must still be realized.

Some early studies were directed to short neutron pulses that excite the state of the top isomers in a solid so that the gamma-ray transitions could benefit from the narrowing of the line from the MÃÆ'¶ssbauer Effect. In conjunction, several benefits are expected from the two stage pumping of the three-tier system. It is estimated that the atomic nucleus, embedded in the near field of the electron-coherent, laser-oscillating electron cloud, will experience a larger dipole field than the driving laser. Furthermore, nonlinearities of oscillating clouds will produce spatial and temporal harmonics, so nuclear transitions of higher multipolarity can also be driven at multipolar frequencies of lasers.

In September 2007, BBC News reported that there was speculation about the possibility of using positronium annihilation to drive very powerful gamma ray laser light. Dr. David Cassidy of the University of California, Riverside proposes that such a single laser can be used to ignite nuclear fusion reactions, replacing the hundreds of lasers currently used in inertial confinement fixation experiments.

Laser X-ray based chamber that is pumped by nuclear explosion has also been proposed as an antimil weapon. Such a device would be a one-shot weapon.

The living cells have been used to produce laser light. Cells are genetically engineered to produce green fluorescent protein (GFP). GFP is used as a "gain medium" laser, in which the amplification of light occurs. The cells are then placed between two small mirrors, just 20 million meters across, which act as "laser cavities" where light can bounce many times through the cell. After bathing the cell with a blue light, it can be seen to emit a directed and intense green laser beam.

src: cdn3.volusion.com

Usage

When lasers were discovered in 1960, they were called "problem-solving solutions". Since then, they have become ubiquitous, finding utilities in thousands of applications that vary widely in every part of modern society, including consumer electronics, information technology, science, medicine, industry, law enforcement, entertainment, and the military. Fiber-optic communication using lasers is a key technology in modern communications, which enables services such as the Internet.

The first use of lasers in everyday life of the general population is the supermarket barcode scanner, introduced in 1974. The laserdisc player, introduced in 1978, was the first successful consumer product to include a laser but the compact disc player was the first-ever laser device to become common, started in 1982 followed immediately by a laser printer.

Some other uses are:

• Communications: in addition to fiber optic communications, lasers are used for free space optical communications, including in-room laser communications.
• Drugs: see below.
• Industry: cutting, welding, material heat treatment, section marking, non-contact part measurement.
• Military: marking targets, guiding ammunition, missile defense, electro-optical countermeasures (EOCM), LIDAR, blinding forces. See below
• Law enforcement: LIDAR traffic enforcement. Lasers are used for latent fingerprint detection in the field of forensic identification
• Research: spectroscopy, laser ablation, laser annealing, laser scattering, laser interferometry, lidar, laser capture microdissection, fluorescence microscopy, metrology.
• Commercial products: laser printer, barcode scanner, thermometer, laser pointer, hologram, bubblegram.
• Entertainment: optical disc, laser lighting screen

In 2004, excluding the laser diode, approximately 131,000 lasers were sold for US $ 2.19 billion. In the same year, about 733 million laser diodes, valued at $ 3.20 billion, were sold.

In medicine

Lasers have many uses in medicine, including laser surgery (especially eye surgery), laser cures, kidney stone treatments, ophthalmoscopy, and cosmetic skin treatments such as acne treatments, cellulite and striae reduction, and hair removal.

Lasers are used to treat cancer by shrinking or destroying tumors or precancerous growth. They are most often used to treat shallow cancers that exist on the surface of the body or layers of internal organs. They are used to treat basal cell skin cancer and the early stages of others such as cervical cell lung cancer, penis, vagina, vulva, and non-small cells. Laser therapy is often combined with other treatments, such as surgery, chemotherapy, or radiation therapy. Laser-induced interstitial thermotherapy (LITT), or interstitial laser photocoagulation, uses lasers to treat some cancers using hyperthermia, which uses heat to shrink tumors by damaging or killing cancer cells. Lasers are more precise than surgery and cause less damage, pain, bleeding, swelling, and scarring. The disadvantage is that the surgeon should have special training. Probably more expensive than other treatments.

As weapon

Lasers of all but the lowest strengths can potentially be used as crippling weapons, through their ability to produce temporary or permanent loss of vision in varying degrees when aimed at the eye. The level, character, and duration of vision impairment caused by exposure to the laser beam vary with laser strength, wavelength (s), collimation of the beam, the exact orientation of the beam, and the duration of exposure. Lasers even a fraction of the watt of the ruling can produce direct, permanent loss of vision under certain conditions, making such a laser a potential non-lethal but crippling weapon. The extreme defect caused by laser blindness makes the use of lasers even as a morally controversial non-lethal weapon, and weapons designed to cause blindness have been banned by the Protocol on Blinding Laser Weapons. The incidents of pilots affected by lasers while flying have prompted the airline authorities to apply specific procedures to deal with such hazards.

Laser weapons capable of directly destroying or destroying targets in combat are still in the experimental stage. The general idea of ​​laser weaponry is to reach targets with short light pulse trains. Rapid evaporation and surface expansion cause shock waves that damage the target. The power required to project this high-powered laser beam is beyond the limits of current mobile power technology, thus supporting dynamic laser gas-driven chemistry. Examples of experimental systems include MIRACL and Tactical High Energy Lasers.

Throughout the 2000s, the United States Air Force worked at Boeing YAL-1, an aerial laser mounted on Boeing 747. The plane was intended to be used to shoot down ballistic missiles entering enemy territory. In March 2009, Northrop Grumman claimed that engineers at Redondo Beach had built and tested an electrically powered solid state laser capable of generating 100 kilowatts, powerful enough to destroy aircraft. According to Brian Strickland, manager for the Solid State Solid Army Solid State Laser program, electrically powered lasers can be installed in aircraft, ships, or other vehicles because they require less space for their support equipment than chemicals. laser. However, the huge power source in mobile applications is still unclear. Ultimately, the project was deemed unfeasible, and canceled in December 2011, with Boeing YAL-1 prototypes being stored and eventually dismantled.

The United States Navy is developing a laser weapon called the Laser Weapon System or LaWS.

Hobbies

In recent years, some fans have been attracted to lasers. Lasers used by hobbyists are generally class IIIa or IIIb (see Salvation), although some have made their own class IV types. However, compared to other hobbyists, laser fans are much less common, due to the costs and potential dangers involved. Because of the cost of lasers, some hobbyists use cheap ways to get lasers, such as saving laser diodes from damaged DVD players (red), Blu-ray (violet) players, or even higher power laser diodes from CD or DVD burners.

Hobbyists have also taken advantage of laser pulseds ​​from retired military applications and modified them to pulsating holography. Pulsed Ruby and YAG laser lasers have been used.

Example with power

Different applications require lasers with different output power. Lasers that produce a continuous beam or series of short pulses can be compared on the basis of their average strength. Lasers that produce pulses can also be characterized on the basis of the strength of each pulse. The peak strength of the pulsing laser is many times greater than its average strength. The average output power is always less than the power consumed.

Examples of high pulsed pulsed systems:

• 700 TW (700ÃÆ' â € "10 ¹² W) - National Ignition Facility, 192-beam laser system, 1.8-megajoule adjacent to the target space of 10 meters in diameter.
• 1.3 PW (1,3ÃÆ' â € "10 ¹⁵ W) - the most powerful laser in the world in 1998, is located at Lawrence Livermore Laboratory

src: cdn.shopify.com

Security

Even the first laser is recognized as potentially dangerous. Theodore Maiman marks the first laser as a single "Gillette" power as it can burn through a Gillette razor blade. Today, it is acceptable that even low-power lasers with only a few milliwatts of output power can be harmful to human vision when they hit the eye directly or after reflection from the shiny surface. At the wavelengths in which the cornea and lens can focus properly, the low coherence and low-light laser range means that it can be focused by the eye to a very small spot on the retina, resulting in local burning and permanent damage in seconds or even less time.

Lasers are usually labeled with a security grade number, which identifies just how dangerous the laser is:

• Class 1 is basically safe, usually because the light is present in the enclosure, for example in the CD player.
• Class 2 is safe during normal use; eye blink reflex will prevent damage. Usually up to 1 mW of power, eg laser pointer.
• Class 3R lasers (formerly IIIa) are usually up to 5 mW and involve a small risk of eye damage in blinking reflex time. Staring at such rays for a few seconds is likely to cause damage to a place in the retina.
• Class 3B may cause eye damage immediately after exposure.
• Class 4 lasers can burn the skin, and in some cases, even scattered light can cause eye and/or skin damage. Many industrial and scientific lasers are in this class.

The indicated strength is for continuous-looking and continuous light-ray lasers. For pulsed lasers and invisible wavelengths, other power limits apply. People working with class 3B and grade 4 lasers can protect their eyes with safety goggles designed to absorb light from certain wavelengths.

Infrared lasers with wavelengths longer than about 1.4 micrometers are often referred to as "eye-safe", because the cornea tends to absorb light at these wavelengths, protecting the retina from damage. The "safe eye" label can be misleading, however, as this only applies to relatively low sustained power waves; high power or Q-switched laser at this wavelength can burn the cornea, cause severe eye damage, and even moderate power lasers can injure the eye.

src: www.thelocal.de

See also

src: ctlasers.com

References

src: www.nightcyclingsafety.com

Further reading

Books

• Bertolotti, Mario (1999, trans. 2004). Laser History . Institute of Physics. ISBNÃ, 0-7503-0911-3.
• Bromberg, Joan Lisa (1991). Laser in America, 1950-1970 . MIT Press. ISBN 978-0-262-02318-4.
• Csele, Mark (2004). Fundamentals of Light and Laser Sources . Wiley. ISBNÃ, 0-471-47660-9.
• Koechner, Walter (1992). Solid-State Laser Engineering . 3rd edition. Springer-Verlag. ISBNÃ, 0-387-53756-2.
• Siegman, Anthony E. (1986). Laser . University Science Book. ISBN: 0-935702-11-3.
• Silfvast, William T. (1996). Laser Fundamentals . Cambridge University Press. ISBN: 0-521-55617-1.
• Svelto, Orazio (1998). Laser Principles . 4th Edition. Trans. David Hanna. Jumper. ISBN: 0-306-45748-2.
• Taylor, Nick (2000). LASER: Inventor, Nobel laureate, and thirty year patent war . New York: Simon & amp; Schuster. ISBN 0-684-83515-0.
• Wilson, J. & amp; Hawkes, J.F.B. (1987). Laser: Principles and Applications . Prentice Hall International Series in Optoelectronics, Prentice Hall. ISBN: 0-13-523697-5.
• Yariv, Amnon (1989). Quantum Electronics . 3rd edition. Wiley. ISBNÃ, 0-471-60997-8.

Periodical

• Applied Physics B: Lasers and Optics (ISSNÃ, 0946-2171)
• Journal of IEEE Wavelight Technology (ISSN 0733-8724)
• IEEE Journal of Quantum Electronics (ISSNÃ, 0018-9197)
• IEEE Journals from Selected Topics in Quantum Electronics (ISSNÃ, 1077-260X)
• IEEE Photonics Technology Letters (ISSN 1041-1135)
• American Optical Society Journal B: Optical Physics (ISSN 0740-3224)
• Laser Focus World (ISSNÃ, 0740-2511)
• Optical Mail (ISSN 0146-9592)
• Photonics Spectra (ISSNÃ, 0731-1230)

src: i.ytimg.com

External links

• Encyclopedia of physics and laser technology by Dr. RÃÆ'¼diger Paschotta
• A Practical Guide for Lasers for Experiments and Fans by Samuel M. Goldwasser
• Homebuilt Laser Page by Professor Mark Csele
• Strong laser is 'the brightest light in the universe' - The world's most powerful laser in 2008 may create supernova shock waves and possibly even antimatter ( New Scientist , April 9, 2008)
• "Laser Fundamentals" online course by prof. F. Balembois and Dr. S. Forget. Instrumentation for Optics , 2008, (accessed January 17, 2014)
• Northrop Grumman Press Release on Firestrike tactical laser product 15 kW.
• Web site about Laser 50th anniversary by APS, OSA, SPIE
• Promote Laser's Laser Birthday Site: Video Interviews, Open Access Articles, Posters, DVDs
• Bright Idea: History of The First Laser of this invention, with an audio interview clip.
• Free software for random laser dynamics simulation
• Demonstration Videos in Lasers and Optics Produced by Massachusetts Institute of Technology (MIT). Real-time effects are indicated in a way that will be hard to see in the classroom settings.
• MIT Video Lecture: Understanding Lasers and Fiber Optics
• The Virtual Laser History Museum, from the touring exhibition by SPIE
The website
• with animations, applications and research on lasers and other phenomena based on quantity Universite Paris Sud

Source of the article : Wikipedia