What does l.a.s.e.r stand for – what does l.a.s.e.r stand for:.What Is a Laser?

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Rajasthan Police. Punjab Police. Punjab Police Jail Warder. CG Vyapam SI. Madras High Court Office Assistant. JK Police Constable. Delhi District Court Group C. Karnataka SDA. PMC Clerk. GPSC Class Odisha CGL. HP Police Constable. Light travels in waves, and the distance between the peaks of a wave is called the wavelength. Each color of light has a different wavelength.

For example, blue light has a shorter wavelength than red light. Sunlight—and the typical light from a lightbulb—is made up of light with many different wavelengths. Our eyes see this mixture of wavelengths as white light.

This animation shows a representation of the different wavelengths present in sunlight. When all of the different wavelengths colors come together, you get white light. Image credit: NASA. A laser is different. Lasers do not occur in nature. However, we have figured ways to artificially create this special type of light. Lasers produce a narrow beam of light in which all of the light waves have very similar wavelengths. This is why laser beams are very narrow, very bright, and can be focused into a very tiny spot.

This animation is a representation of in phase laser light waves. Because laser light stays focused and does not spread out much like a flashlight would , laser beams can travel very long distances. On May 16, , Theodore H. Maiman’s functional laser used a flashlamp -pumped synthetic ruby crystal to produce red laser light at nanometers wavelength. The device was only capable of pulsed operation, due to its three-level pumping design scheme. Bennett , and Donald Herriott , constructed the first gas laser , using helium and neon that was capable of continuous operation in the infrared U.

Basov and Javan proposed the semiconductor laser diode concept. In , Robert N. Hall demonstrated the first laser diode device, which was made of gallium arsenide and emitted in the near- infrared band of the spectrum at nm. Later that year, Nick Holonyak , Jr. This first semiconductor laser could only be used in pulsed-beam operation, and when cooled to liquid nitrogen temperatures 77 K.

Since the early period of laser history, laser research has produced a variety of improved and specialized laser types, optimized for different performance goals, including:. In , researchers made a white laser, whose light is modulated by a synthetic nanosheet made out of zinc, cadmium, sulfur, and selenium that can emit red, green, and blue light in varying proportions, with each wavelength spanning nm.

The device has potential for applications in quantum computing. Following the invention of the HeNe gas laser, many other gas discharges have been found to amplify light coherently.

Gas lasers using many different gases have been built and used for many purposes. The helium—neon laser HeNe is able to operate at a number of different wavelengths, however the vast majority are engineered to lase at nm; these relatively low cost but highly coherent lasers are extremely common in optical research and educational laboratories.

Commercial carbon dioxide CO 2 lasers can emit many hundreds of watts in a single spatial mode which can be concentrated into a tiny spot. This emission is in the thermal infrared at Depending on the optical design one or more of these transitions can be lasing simultaneously; the most commonly used lines are nm, nm and A nitrogen transverse electrical discharge in gas at atmospheric pressure TEA laser is an inexpensive gas laser, often home-built by hobbyists, which produces rather incoherent UV light at Helium -silver HeAg nm and neon -copper NeCu nm are two examples.

Like all low-pressure gas lasers, the gain media of these lasers have quite narrow oscillation linewidths , less than 3 GHz 0. Lasing without maintaining the medium excited into a population inversion was demonstrated in in sodium gas and again in in rubidium gas by various international teams. Chemical lasers are powered by a chemical reaction permitting a large amount of energy to be released quickly.

Such very high power lasers are especially of interest to the military, however continuous wave chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some industrial applications. As examples, in the hydrogen fluoride laser — nm and the deuterium fluoride laser nm the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride.

Excimer lasers are a special sort of gas laser powered by an electric discharge in which the lasing medium is an excimer , or more precisely an exciplex in existing designs.

These are molecules which can only exist with one atom in an excited electronic state. Once the molecule transfers its excitation energy to a photon, its atoms are no longer bound to each other and the molecule disintegrates. This drastically reduces the population of the lower energy state thus greatly facilitating a population inversion.

Excimers currently used are all noble gas compounds ; noble gasses 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.

Solid-state lasers use a crystalline or glass rod which is “doped” with ions that provide the required energy states. For example, the first working laser was a ruby laser , made from ruby chromium -doped corundum. The population inversion is actually maintained in the dopant. These materials are pumped optically using a shorter wavelength than the lasing wavelength, often from a flashtube or from another laser.

The usage of the term “solid-state” in laser physics is narrower than in typical use. Semiconductor lasers laser diodes are typically not referred to as solid-state lasers. All these lasers can produce high powers in the infrared spectrum at nm. They are used for cutting, welding and marking of metals and other materials, and also in spectroscopy and for pumping dye lasers. These lasers are also commonly frequency doubled , tripled or quadrupled to produce nm green, visible , nm and nm UV beams, respectively.

Frequency-doubled diode-pumped solid-state DPSS lasers are used to make bright green laser pointers. Ytterbium , holmium , thulium , and erbium are other common “dopants” in solid-state lasers. They are potentially very efficient and high powered due to a small quantum defect. Extremely high powers in ultrashort pulses can be achieved with Yb:YAG. Holmium -doped YAG crystals emit at nm and form an efficient laser operating at infrared wavelengths strongly absorbed by water-bearing tissues.

The Ho-YAG is usually operated in a pulsed mode, and passed through optical fiber surgical devices to resurface joints, remove rot from teeth, vaporize cancers, and pulverize kidney and gall stones.

Titanium -doped sapphire Ti:sapphire produces a highly tunable infrared laser, commonly used for spectroscopy. It is also notable for use as a mode-locked laser producing ultrashort pulses of extremely high peak power. Thermal limitations in solid-state lasers arise from unconverted pump power that heats the medium. Diode-pumped thin disk lasers overcome these issues by having a gain medium that is much thinner than the diameter of the pump beam.

This allows for a more uniform temperature in the material. Thin disk lasers have been shown to produce beams of up to one kilowatt. Solid-state lasers or laser amplifiers where the light is guided due to the total internal reflection in a single mode optical fiber are instead called fiber lasers. Guiding of light allows extremely long gain regions providing good cooling conditions; fibers have high surface area to volume ratio which allows efficient cooling.

In addition, the fiber’s waveguiding properties tend to reduce thermal distortion of the beam. Erbium and ytterbium ions are common active species in such lasers. Quite often, the fiber laser is designed as a double-clad fiber. This type of fiber consists of a fiber core, an inner cladding and an outer cladding. The index of the three concentric layers is chosen so that the fiber core acts as a single-mode fiber for the laser emission while the outer cladding acts as a highly multimode core for the pump laser.

This lets the pump propagate a large amount of power into and through the active inner core region, while still having a high numerical aperture NA to have easy launching conditions. Pump light can be used more efficiently by creating a fiber disk laser , or a stack of such lasers.

This effect is called photodarkening. In bulk laser materials, the cooling is not so efficient, and it is difficult to separate the effects of photodarkening from the thermal effects, but the experiments in fibers show that the photodarkening can be attributed to the formation of long-living color centers.

Photonic crystal lasers are lasers based on nano-structures that provide the mode confinement and the density of optical states DOS structure required for the feedback to take place.

Semiconductor lasers are diodes which are electrically pumped. Recombination of electrons and holes created by the applied current introduces optical gain. Reflection from the ends of the crystal form an optical resonator, although the resonator can be external to the semiconductor in some designs. Commercial laser diodes emit at wavelengths from nm to nm. Laser diodes are also frequently used to optically pump other lasers with high efficiency. The highest power industrial laser diodes, with power up to 20 kW, are used in industry for cutting and welding.

These devices can generate high power outputs with good beam quality, wavelength-tunable narrow- linewidth radiation, or ultrashort laser pulses. Vertical cavity surface-emitting lasers VCSELs are semiconductor lasers whose emission direction is perpendicular to the surface of the wafer. VCSEL devices typically have a more circular output beam than conventional laser diodes.

Quantum cascade lasers are semiconductor lasers that have an active transition between energy sub-bands of an electron in a structure containing several quantum wells. The development of a silicon laser is important in the field of optical computing. Silicon is the material of choice for integrated circuits , and so electronic and silicon photonic components such as optical interconnects could be fabricated on the same chip.

Unfortunately, silicon is a difficult lasing material to deal with, since it has certain properties which block lasing. However, recently teams have produced silicon lasers through methods such as fabricating the lasing material from silicon and other semiconductor materials, such as indium III phosphide or gallium III arsenide , materials which allow coherent light to be produced from silicon.

These are called hybrid silicon laser. Recent developments have also shown the use of monolithically integrated nanowire lasers directly on silicon for optical interconnects, paving the way for chip level applications. Dye lasers use an organic dye as the gain medium. The wide gain spectrum of available dyes, or mixtures of dyes, allows these lasers to be highly tunable, or to produce very short-duration pulses on the order of a few femtoseconds.

Although these tunable lasers are mainly known in their liquid form, researchers have also demonstrated narrow-linewidth tunable emission in dispersive oscillator configurations incorporating solid-state dye gain media. In their most prevalent form these solid state dye lasers use dye-doped polymers as laser media.

Free-electron lasers , or FELs, generate coherent, high power radiation that is widely tunable, currently ranging in wavelength from microwaves through terahertz radiation and infrared to the visible spectrum, to soft X-rays. They have the widest frequency range of any laser type. While FEL beams share the same optical traits as other lasers, such as coherent radiation, FEL operation is quite different. Unlike gas, liquid, or solid-state lasers, which rely on bound atomic or molecular states, FELs use a relativistic electron beam as the lasing medium, hence the term free-electron.

The pursuit of a high-quantum-energy laser using transitions between isomeric states of an atomic nucleus has been the subject of wide-ranging academic research since the early s. Much of this is summarized in three review articles. While many scientists remain optimistic that a breakthrough is near, an operational gamma-ray laser is yet to be realized.

In September , the BBC News reported that there was speculation about the possibility of using positronium annihilation to drive a very powerful gamma ray laser. David Cassidy of the University of California, Riverside proposed that a single such laser could be used to ignite a nuclear fusion reaction, replacing the banks of hundreds of lasers currently employed in inertial confinement fusion experiments.

Space-based X-ray lasers pumped by a nuclear explosion have also been proposed as antimissile weapons. Living cells have been used to produce laser light. The cells were then placed between two 20 micrometer wide mirrors, which acted as the laser cavity. When the cell was illuminated with blue light, it emitted intense, directed green laser light.

Like astrophysical masers , irradiated planetary or stellar gases may amplify light producing a natural laser. When lasers were invented in , they were called “a solution looking for a problem”.

Fiber-optic communication using lasers is a key technology in modern communications, allowing services such as the Internet. The first widely noticeable use of lasers was the supermarket barcode scanner , introduced in The laserdisc player, introduced in , was the first successful consumer product to include a laser but the compact disc player was the first laser-equipped device to become common, beginning in followed shortly by laser printers.

Lasers have many uses in medicine, including laser surgery particularly eye surgery , laser healing photobiomodulation therapy , kidney stone treatment, ophthalmoscopy , and cosmetic skin treatments such as acne treatment, cellulite and striae reduction, and hair removal. Lasers are used to treat cancer by shrinking or destroying tumors or precancerous growths. They are most commonly used to treat superficial cancers that are on the surface of the body or the lining of internal organs.

They are used to treat basal cell skin cancer and the very early stages of others like cervical , penile , vaginal , vulvar , and non-small cell lung cancer. 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 traditional surgery methods and cause less damage, pain, bleeding , swelling, and scarring.

A disadvantage is that surgeons must acquire specialized training and thus it will likely be more expensive than other treatments. A laser weapon is a laser that is used as a directed-energy weapon. In recent years, some hobbyists have taken an interest in lasers. Due to the cost of lasers, some hobbyists use inexpensive means to obtain lasers, such as salvaging laser diodes from broken DVD players red , Blu-ray players violet , or even higher power laser diodes from CD or DVD burners.

Hobbyists have also used surplus lasers taken from retired military applications and modified them for holography. Pulsed ruby and YAG lasers work well for this application. Different applications need lasers with different output powers. Lasers that produce a continuous beam or a series of short pulses can be compared on the basis of their average power. Lasers that produce pulses can also be characterized based on the peak power of each pulse. The peak power of a pulsed laser is many orders of magnitude greater than its average power.

The average output power is always less than the power consumed. Even the first laser was recognized as being potentially dangerous. Theodore Maiman characterized the first laser as having a power of one “Gillette” as it could burn through one Gillette razor blade.

Today, it is accepted that even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight when the beam hits the eye directly or after reflection from a shiny surface. At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina , resulting in localized burning and permanent damage in seconds or even less time.

Lasers are usually labeled with a safety class number, which identifies how dangerous the laser is:. The indicated powers are for visible-light, continuous-wave lasers. For pulsed lasers and invisible wavelengths, other power limits apply. People working with class 3B and class 4 lasers can protect their eyes with safety goggles which are designed to absorb light of a particular wavelength. Infrared lasers with wavelengths longer than about 1.

The label “eye-safe” can be misleading, however, as it applies only to relatively low power continuous wave beams; a high power or Q-switched laser at these wavelengths can burn the cornea, causing severe eye damage, and even moderate power lasers can injure the eye. Lasers can be a hazard to both civil and military aviation, due to the potential to temporarily distract or blind pilots. See Lasers and aviation safety for more on this topic. Cameras based on charge-coupled devices may actually be more sensitive to laser damage than biological eyes.

From Wikipedia, the free encyclopedia. Device which emits light via optical amplification. For other uses, see Laser disambiguation. For uses of “Laze”, see Laze. Main article: Laser construction. Gain medium Laser pumping energy High reflector Output coupler Laser beam.

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. May Learn how and when to remove this template message. See also: Laser science. Main article: Stimulated emission.

Main article: Pulsed laser. Main article: Q-switching. Main article: Mode locking. Main article: Maser.

Further information: List of laser types. Main article: Gas laser. Main article: Fiber laser. Main article: Semiconductor lasers. Main article: List of applications for lasers. Main articles: Laser medicine and Lasers in cancer treatment.

Main article: Laser weapon. This article should include a summary of Laser weapon. See Wikipedia:Summary style for information on how to incorporate it into this article’s main text.

December Main article: Laser safety. Left: European laser warning symbol required for Class 2 lasers and higher. Right: US laser warning label, in this case for a Class 3B laser. Retrieved May 18, Merriam Webster.

 
 

– What does l.a.s.e.r stand for – what does l.a.s.e.r stand for:

 

The letters in the word laser stand for L ight A mplification by S timulated E mission of R adiation. A laser is an unusual light source. It is quite different from a light bulb or a flash light. Lasers produce a very narrow beam of light. This type of light is useful for lots of technologies and instruments—even some that you might use at home!

Light travels in waves, and the distance between the peaks of a wave is called the wavelength. Each color of light has a different wavelength. For example, blue light has a shorter wavelength than red light. Sunlight—and the typical light from a lightbulb—is made up of light with many different wavelengths.

Our eyes see this mixture of wavelengths as white light. This animation shows a representation of the different wavelengths present in sunlight. When all of the different wavelengths colors come together, you get white light. Image credit: NASA.

A laser is different. Lasers do not occur in nature. However, we have figured ways to artificially create this special type of light. Lasers produce a narrow beam of light in which all of the light waves have very similar wavelengths. This is why laser beams are very narrow, very bright, and can be focused into a very tiny spot.

This animation is a representation of in phase по этому адресу light waves. Because laser light stays focused and does not spread out much like a flashlight wouldlaser beams can travel very long distances. They can also concentrate a lot of energy on a very small area.

This animation shows how a посетить страницу источник can focus what does l.a.s.e.r stand for – what does l.a.s.e.r stand for: of its light into one small point. Credit: NASA. Lasers have many uses. They are used in precision tools and can cut through diamonds or thick metal. They can also be designed to help in delicate surgeries. /8088.txt are used for recording and retrieving information.

They are used in communications and in carrying TV and internet signals. We also find them in laser printers, bar code scanners, and DVD players. They also help to make parts for computers and other electronics. Lasers are also used in instruments called spectrometers. Spectrometers can help нажмите чтобы прочитать больше figure out what things are made of. For example, the Curiosity rover uses a laser spectrometer to see what kinds of детальнее на этой странице are in certain rocks on Mars.

By zapping tiny holes in Martian soil and rock, ChemCam can determine what the material is made of. Lasers have also been used in instruments that map the surfaces of planets, moons, and asteroids.

Scientists have even measured the distance between the moon and Earth using lasers! By measuring the amount of time ссылка на страницу takes for a laser beam to travel to the moon and back, astronomers can tell exactly how far away it is!

What does l.a.s.e.r stand for – what does l.a.s.e.r stand for: Is a Laser? The Short Answer:. A laser produces a very narrow beam of light that is useful in many technologies and instruments.

More about technology! Learn what does l.a.s.e.r stand for – what does l.a.s.e.r stand for: the Mars Rovers! How does GPS work? Where do satellites go when they die? Welcome to Space Place Live! Lucy’s Planet Hunt. More Less.

 

What does l.a.s.e.r stand for – what does l.a.s.e.r stand for:. What does the word laser stand for to begin with?

 

Retrieve it. Abbreviation » Term. Term » Abbreviation. Word in Term. Term » Abbr. Filter by: Select category from list Notify me of new comments via email. Like Reply Report 3 years ago. Like Reply Report 5 years ago. Like Reply Report 1 7 years ago. Like Reply Report 8 years ago. Cancel Report. Create a new account. Log In. Don’t keep it to yourself! Add it HERE! Still can’t find the acronym definition you were looking for?

Use our Power Search technology to look for more unique definitions from across the web! Search the web. Citation Use the citation options below to add these abbreviations to your bibliography. Pump light may be provided by a flash lamp or by another laser. The most common type of laser uses feedback from an optical cavity —a pair of mirrors on either end of the gain medium.

Light bounces back and forth between the mirrors, passing through the gain medium and being amplified each time. Typically one of the two mirrors, the output coupler , is partially transparent. Some of the light escapes through this mirror. Depending on the design of the cavity whether the mirrors are flat or curved , the light coming out of the laser may spread out or form a narrow beam. In analogy to electronic oscillators , this device is sometimes called a laser oscillator.

Most practical lasers contain additional elements that affect properties of the emitted light, such as the polarization, wavelength, and shape of the beam. Electrons and how they interact with electromagnetic fields are important in our understanding of chemistry and physics.

In the classical view , the energy of an electron orbiting an atomic nucleus is larger for orbits further from the nucleus of an atom. However, quantum mechanical effects force electrons to take on discrete positions in orbitals. Thus, electrons are found in specific energy levels of an atom, two of which are shown below:.

An electron in an atom can absorb energy from light photons or heat phonons only if there is a transition between energy levels that matches the energy carried by the photon or phonon. For light, this means that any given transition will only absorb one particular wavelength of light. Photons with the correct wavelength can cause an electron to jump from the lower to the higher energy level. The photon is consumed in this process. Conserving energy, the electron transitions to a lower energy level which is not occupied, with transitions to different levels having different time constants.

This process is called ” spontaneous emission “. Spontaneous emission is a quantum-mechanical effect and a direct physical manifestation of the Heisenberg uncertainty principle.

The emitted photon has random direction, but its wavelength matches the absorption wavelength of the transition. This is the mechanism of fluorescence and thermal emission. A photon with the correct wavelength to be absorbed by a transition can also cause an electron to drop from the higher to the lower level, emitting a new photon. The emitted photon exactly matches the original photon in wavelength, phase, and direction. This process is called stimulated emission. The gain medium is put into an excited state by an external source of energy.

In most lasers this medium consists of a population of atoms which have been excited into such a state by means of an outside light source, or an electrical field which supplies energy for atoms to absorb and be transformed into their excited states. The gain medium of a laser is normally a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission described above. This material can be of any state : gas, liquid, solid, or plasma.

The gain medium absorbs pump energy, which raises some electrons into higher-energy ” excited ” quantum states. Particles can interact with light by either absorbing or emitting photons. Emission can be spontaneous or stimulated. In the latter case, the photon is emitted in the same direction as the light that is passing by.

When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved. In this state, the rate of stimulated emission is larger than the rate of absorption of light in the medium, and therefore the light is amplified. A system with this property is called an optical amplifier. When an optical amplifier is placed inside a resonant optical cavity, one obtains a laser.

For lasing media with extremely high gain, so-called superluminescence , it is possible for light to be sufficiently amplified in a single pass through the gain medium without requiring a resonator.

Although often referred to as a laser see for example nitrogen laser , [19] the light output from such a device lacks the spatial and temporal coherence achievable with lasers. Such a device cannot be described as an oscillator but rather is a high gain optical amplifier which amplifies its own spontaneous emission. The optical resonator is sometimes referred to as an “optical cavity”, but this is a misnomer: lasers use open resonators as opposed to the literal cavity that would be employed at microwave frequencies in a maser.

The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting back on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain amplification in the medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially.

But each stimulated emission event returns an atom from its excited state to the ground state, reducing the gain of the medium. With increasing beam power the net gain gain minus loss reduces to unity and the gain medium is said to be saturated. In a continuous wave CW laser, the balance of pump power against gain saturation and cavity losses produces an equilibrium value of the laser power inside the cavity; this equilibrium determines the operating point of the laser.

If the applied pump power is too small, the gain will never be sufficient to overcome the cavity losses, and laser light will not be produced. The minimum pump power needed to begin laser action is called the lasing threshold. The gain medium will amplify any photons passing through it, regardless of direction; but only the photons in a spatial mode supported by the resonator will pass more than once through the medium and receive substantial amplification.

In most lasers, lasing begins with spontaneous emission into the lasing mode. This initial light is then amplified by stimulated emission in the gain medium.

Stimulated emission produces light that matches the input signal in direction, wavelength, and polarization, whereas the phase of emitted light is 90 degrees in lead of the stimulating light. The fundamental laser linewidth [21] of light emitted from the lasing resonator can be orders of magnitude narrower than the linewidth of light emitted from the passive resonator.

Some lasers use a separate injection seeder to start the process off with a beam that is already highly coherent. This can produce beams with a narrower spectrum than would otherwise be possible.

In , Roy J. Glauber showed that coherent states are formed from combinations of photon number states, for which he was awarded the Nobel Prize in physics. As a result, the arrival rate of photons in a laser beam is described by Poisson statistics. Many lasers produce a beam that can be approximated as a Gaussian beam ; such beams have the minimum divergence possible for a given beam diameter.

Some lasers, particularly high-power ones, produce multimode beams, with the transverse modes often approximated using Hermite — Gaussian or Laguerre -Gaussian functions. Some high power lasers use a flat-topped profile known as a ” tophat beam “. Unstable laser resonators not used in most lasers produce fractal-shaped beams.

Near the “waist” or focal region of a laser beam, it is highly collimated : the wavefronts are planar, normal to the direction of propagation, with no beam divergence at that point. However, due to diffraction , that can only remain true well within the Rayleigh range. The beam of a single transverse mode gaussian beam laser eventually diverges at an angle which varies inversely with the beam diameter, as required by diffraction theory.

Thus, the “pencil beam” directly generated by a common helium—neon laser would spread out to a size of perhaps kilometers when shone on the Moon from the distance of the earth. However even such a divergent beam can be transformed into a similarly collimated beam by means of a lens system, as is always included, for instance, in a laser pointer whose light originates from a laser diode. That is possible due to the light being of a single spatial mode.

This unique property of laser light, spatial coherence , cannot be replicated using standard light sources except by discarding most of the light as can be appreciated by comparing the beam from a flashlight torch or spotlight to that of almost any laser.

A laser beam profiler is used to measure the intensity profile, width, and divergence of laser beams. Diffuse reflection of a laser beam from a matte surface produces a speckle pattern with interesting properties. The mechanism of producing radiation in a laser relies on stimulated emission , where energy is extracted from a transition in an atom or molecule. This is a quantum phenomenon [ dubious — discuss ] that was predicted by Albert Einstein , who derived the relationship between the A coefficient describing spontaneous emission and the B coefficient which applies to absorption and stimulated emission.

However, in the case of the free electron laser , atomic energy levels are not involved; it appears that the operation of this rather exotic device can be explained without reference to quantum mechanics.

A laser can be classified as operating in either continuous or pulsed mode, depending on whether the power output is essentially continuous over time or whether its output takes the form of pulses of light on one or another time scale.

Of course even a laser whose output is normally continuous can be intentionally turned on and off at some rate in order to create pulses of light. When the modulation rate is on time scales much slower than the cavity lifetime and the time period over which energy can be stored in the lasing medium or pumping mechanism, then it is still classified as a “modulated” or “pulsed” continuous wave laser.

Most laser diodes used in communication systems fall in that category. Some applications of lasers depend on a beam whose output power is constant over time. Such a laser is known as continuous-wave CW laser. Many types of lasers can be made to operate in continuous-wave mode to satisfy such an application. Many of these lasers actually lase in several longitudinal modes at the same time, and beats between the slightly different optical frequencies of those oscillations will, in fact, produce amplitude variations on time scales shorter than the round-trip time the reciprocal of the frequency spacing between modes , typically a few nanoseconds or less.

In most cases, these lasers are still termed “continuous-wave” as their output power is steady when averaged over any longer time periods, with the very high-frequency power variations having little or no impact in the intended application. However, the term is not applied to mode-locked lasers, where the intention is to create very short pulses at the rate of the round-trip time. For continuous-wave operation, it is required for the population inversion of the gain medium to be continually replenished by a steady pump source.

In some lasing media, this is impossible. In some other lasers, it would require pumping the laser at a very high continuous power level, which would be impractical or destroy the laser by producing excessive heat.

Such lasers cannot be run in CW mode. Pulsed operation of lasers refers to any laser not classified as continuous wave, so that the optical power appears in pulses of some duration at some repetition rate. This encompasses a wide range of technologies addressing a number of different motivations.

Some lasers are pulsed simply because they cannot be run in continuous mode. In other cases, the application requires the production of pulses having as large an energy as possible. Since the pulse energy is equal to the average power divided by the repetition rate, this goal can sometimes be satisfied by lowering the rate of pulses so that more energy can be built up in between pulses.

In laser ablation , for example, a small volume of material at the surface of a work piece can be evaporated if it is heated in a very short time, while supplying the energy gradually would allow for the heat to be absorbed into the bulk of the piece, never attaining a sufficiently high temperature at a particular point. Other applications rely on the peak pulse power rather than the energy in the pulse , especially in order to obtain nonlinear optical effects.

For a given pulse energy, this requires creating pulses of the shortest possible duration utilizing techniques such as Q-switching. The optical bandwidth of a pulse cannot be narrower than the reciprocal of the pulse width. In the case of extremely short pulses, that implies lasing over a considerable bandwidth, quite contrary to the very narrow bandwidths typical of CW lasers.

In a Q-switched laser, the population inversion is allowed to build up by introducing loss inside the resonator which exceeds the gain of the medium; this can also be described as a reduction of the quality factor or ‘Q’ of the cavity.

Then, after 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 rapidly removed or that occurs by itself in a passive device , allowing lasing to begin which rapidly obtains the stored energy in the gain medium. This results in a short pulse incorporating that energy, and thus a high peak power. A mode-locked laser is capable of emitting extremely short pulses on the order of tens of picoseconds down to less than 10 femtoseconds.

These pulses repeat at the round-trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator. Due to the Fourier limit also known as energy—time uncertainty , a pulse of such short temporal length has a spectrum spread over a considerable bandwidth. Thus such a gain medium must have a gain bandwidth sufficiently broad to amplify those frequencies.

An example of a suitable material is titanium -doped, artificially grown sapphire Ti:sapphire , which has a very wide gain bandwidth and can thus produce pulses of only a few femtoseconds duration. Such mode-locked lasers are a most versatile tool for researching processes occurring on extremely short time scales known as femtosecond physics, femtosecond chemistry and ultrafast science , for maximizing the effect of nonlinearity in optical materials e.

Unlike the giant pulse of a Q-switched laser, consecutive pulses from a mode-locked laser are phase-coherent, that is, the pulses and not just their envelopes are identical and perfectly periodic. For this reason, and the extremely large peak powers attained by such short pulses, such lasers are invaluable in certain areas of research.

Another method of achieving pulsed laser operation is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flash lamps, or another laser which is already pulsed. Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a dye molecule was so short that a high energy, fast pump was needed. The way to overcome this problem was to charge up large capacitors which are then switched to discharge through flashlamps, producing an intense flash.

Pulsed pumping is also required for three-level lasers in which the lower energy level rapidly becomes highly populated preventing further lasing until those atoms relax to the ground state. These lasers, such as the excimer laser and the copper vapor laser, can never be operated in CW mode.

In , Albert Einstein established the theoretical foundations for the laser and the maser in the paper Zur Quantentheorie der Strahlung On the Quantum Theory of Radiation via a re-derivation of Max Planck ‘s law of radiation, conceptually based upon probability coefficients Einstein coefficients for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation.

Ladenburg confirmed the existence of the phenomena of stimulated emission and negative absorption. Fabrikant predicted the use of stimulated emission to amplify “short” waves.

Lamb and R. Retherford found apparent stimulated emission in hydrogen spectra and effected the first demonstration of stimulated emission. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave radiation rather than infrared or visible radiation. Townes’s maser was incapable of continuous output. These gain media could release stimulated emissions between an excited state and a lower excited state, not the ground state, facilitating the maintenance of a population inversion.

In , Prokhorov and Basov suggested optical pumping of a multi-level system as a method for obtaining the population inversion, later a main method of laser pumping. Townes reports that several eminent physicists—among them Niels Bohr , John von Neumann , and Llewellyn Thomas —argued the maser violated Heisenberg’s uncertainty principle and hence could not work.

Others such as Isidor Rabi and Polykarp Kusch expected that it would be impractical and not worth the effort. 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 construction of oscillators and amplifiers based on the maser—laser principle”.

In April , Japanese engineer Jun-ichi Nishizawa proposed the concept of a ” semiconductor optical maser ” in a patent application. As ideas developed, they abandoned infrared radiation to instead concentrate on visible light. In , Bell Labs filed a patent application for their proposed optical maser; and Schawlow and Townes submitted a manuscript of their theoretical calculations to the Physical Review , which was published in Simultaneously, at Columbia University , graduate student Gordon Gould was working on a doctoral thesis about the energy levels of excited thallium.

When Gould and Townes met, they spoke of radiation emission , as a general subject; afterwards, in November , Gould noted his ideas for a “laser”, including using an open resonator later an essential laser-device component. Moreover, in , Prokhorov independently proposed using an open resonator, the first published appearance of this idea. Meanwhile, Schawlow and Townes had decided on an open-resonator laser design — apparently unaware of Prokhorov’s publications and Gould’s unpublished laser work.

Gould’s notes included possible applications for a laser, such as spectrometry , interferometry , radar , and nuclear fusion. He continued developing the idea, and filed a patent application in April The U.

Patent Office denied his application, and awarded a patent to Bell Labs , in That provoked a twenty-eight-year lawsuit , featuring scientific prestige and money as the stakes. Gould won his first minor patent in , yet it was not until that he won the first significant patent lawsuit victory, when a Federal judge ordered the U. Patent Office to issue patents to Gould for the optically pumped and the gas discharge laser devices.

The question of just how to assign credit for inventing the laser remains unresolved by historians. On May 16, , Theodore H. Maiman’s functional laser used a flashlamp -pumped synthetic ruby crystal to produce red laser light at nanometers wavelength. The device was only capable of pulsed operation, due to its three-level pumping design scheme.

Bennett , and Donald Herriott , constructed the first gas laser , using helium and neon that was capable of continuous operation in the infrared U.

Basov and Javan proposed the semiconductor laser diode concept. In , Robert N. Hall demonstrated the first laser diode device, which was made of gallium arsenide and emitted in the near- infrared band of the spectrum at nm. Later that year, Nick Holonyak , Jr.

This first semiconductor laser could only be used in pulsed-beam operation, and when cooled to liquid nitrogen temperatures 77 K. Since the early period of laser history, laser research has produced a variety of improved and specialized laser types, optimized for different performance goals, including:. In , researchers made a white laser, whose light is modulated by a synthetic nanosheet made out of zinc, cadmium, sulfur, and selenium that can emit red, green, and blue light in varying proportions, with each wavelength spanning nm.

The device has potential for applications in quantum computing. Following the invention of the HeNe gas laser, many other gas discharges have been found to amplify light coherently. Gas lasers using many different gases have been built and used for many purposes.

The helium—neon laser HeNe is able to operate at a number of different wavelengths, however the vast majority are engineered to lase at nm; these relatively low cost but highly coherent lasers are extremely common in optical research and educational laboratories. Commercial carbon dioxide CO 2 lasers can emit many hundreds of watts in a single spatial mode which can be concentrated into a tiny spot.

This emission is in the thermal infrared at Depending on the optical design one or more of these transitions can be lasing simultaneously; the most commonly used lines are nm, nm and A nitrogen transverse electrical discharge in gas at atmospheric pressure TEA laser is an inexpensive gas laser, often home-built by hobbyists, which produces rather incoherent UV light at Helium -silver HeAg nm and neon -copper NeCu nm are two examples.

Like all low-pressure gas lasers, the gain media of these lasers have quite narrow oscillation linewidths , less than 3 GHz 0. Lasing without maintaining the medium excited into a population inversion was demonstrated in in sodium gas and again in in rubidium gas by various international teams.

Chemical lasers are powered by a chemical reaction permitting a large amount of energy to be released quickly. Such very high power lasers are especially of interest to the military, however continuous wave chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some industrial applications.

As examples, in the hydrogen fluoride laser — nm and the deuterium fluoride laser nm the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride. Excimer lasers are a special sort of gas laser powered by an electric discharge in which the lasing medium is an excimer , or more precisely an exciplex in existing designs. These are molecules which can only exist with one atom in an excited electronic state.

Once the molecule transfers its excitation energy to a photon, its atoms are no longer bound to each other and the molecule disintegrates. This drastically reduces the population of the lower energy state thus greatly facilitating a population inversion. Excimers currently used are all noble gas compounds ; noble gasses 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.

Solid-state lasers use a crystalline or glass rod which is “doped” with ions that provide the required energy states. For example, the first working laser was a ruby laser , made from ruby chromium -doped corundum. The population inversion is actually maintained in the dopant. These materials are pumped optically using a shorter wavelength than the lasing wavelength, often from a flashtube or from another laser. The usage of the term “solid-state” in laser physics is narrower than in typical use.

Semiconductor lasers laser diodes are typically not referred to as solid-state lasers. All these lasers can produce high powers in the infrared spectrum at nm. They are used for cutting, welding and marking of metals and other materials, and also in spectroscopy and for pumping dye lasers.

These lasers are also commonly frequency doubled , tripled or quadrupled to produce nm green, visible , nm and nm UV beams, respectively. Frequency-doubled diode-pumped solid-state DPSS lasers are used to make bright green laser pointers. Ytterbium , holmium , thulium , and erbium are other common “dopants” in solid-state lasers.

They are potentially very efficient and high powered due to a small quantum defect. Extremely high powers in ultrashort pulses can be achieved with Yb:YAG. Holmium -doped YAG crystals emit at nm and form an efficient laser operating at infrared wavelengths strongly absorbed by water-bearing tissues.

The Ho-YAG is usually operated in a pulsed mode, and passed through optical fiber surgical devices to resurface joints, remove rot from teeth, vaporize cancers, and pulverize kidney and gall stones. Titanium -doped sapphire Ti:sapphire produces a highly tunable infrared laser, commonly used for spectroscopy.

It is also notable for use as a mode-locked laser producing ultrashort pulses of extremely high peak power. Thermal limitations in solid-state lasers arise from unconverted pump power that heats the medium. Diode-pumped thin disk lasers overcome these issues by having a gain medium that is much thinner than the diameter of the pump beam.

This allows for a more uniform temperature in the material. Thin disk lasers have been shown to produce beams of up to one kilowatt. Solid-state lasers or laser amplifiers where the light is guided due to the total internal reflection in a single mode optical fiber are instead called fiber lasers.

Guiding of light allows extremely long gain regions providing good cooling conditions; fibers have high surface area to volume ratio which allows efficient cooling. In addition, the fiber’s waveguiding properties tend to reduce thermal distortion of the beam. Erbium and ytterbium ions are common active species in such lasers. Quite often, the fiber laser is designed as a double-clad fiber. This type of fiber consists of a fiber core, an inner cladding and an outer cladding.

The index of the three concentric layers is chosen so that the fiber core acts as a single-mode fiber for the laser emission while the outer cladding acts as a highly multimode core for the pump laser. This lets the pump propagate a large amount of power into and through the active inner core region, while still having a high numerical aperture NA to have easy launching conditions.

Pump light can be used more efficiently by creating a fiber disk laser , or a stack of such lasers. This effect is called photodarkening. In bulk laser materials, the cooling is not so efficient, and it is difficult to separate the effects of photodarkening from the thermal effects, but the experiments in fibers show that the photodarkening can be attributed to the formation of long-living color centers.

Photonic crystal lasers are lasers based on nano-structures that provide the mode confinement and the density of optical states DOS structure required for the feedback to take place. Semiconductor lasers are diodes which are electrically pumped. Recombination of electrons and holes created by the applied current introduces optical gain.

Reflection from the ends of the crystal form an optical resonator, although the resonator can be external to the semiconductor in some designs. Commercial laser diodes emit at wavelengths from nm to nm. Laser diodes are also frequently used to optically pump other lasers with high efficiency. The highest power industrial laser diodes, with power up to 20 kW, are used in industry for cutting and welding. These devices can generate high power outputs with good beam quality, wavelength-tunable narrow- linewidth radiation, or ultrashort laser pulses.

Vertical cavity surface-emitting lasers VCSELs are semiconductor lasers whose emission direction is perpendicular to the surface of the wafer. VCSEL devices typically have a more circular output beam than conventional laser diodes.

Quantum cascade lasers are semiconductor lasers that have an active transition between energy sub-bands of an electron in a structure containing several quantum wells. The development of a silicon laser is important in the field of optical computing.

Silicon is the material of choice for integrated circuits , and so electronic and silicon photonic components such as optical interconnects could be fabricated on the same chip. Unfortunately, silicon is a difficult lasing material to deal with, since it has certain properties which block lasing. However, recently teams have produced silicon lasers through methods such as fabricating the lasing material from silicon and other semiconductor materials, such as indium III phosphide or gallium III arsenide , materials which allow coherent light to be produced from silicon.

These are called hybrid silicon laser. Recent developments have also shown the use of monolithically integrated nanowire lasers directly on silicon for optical interconnects, paving the way for chip level applications. Dye lasers use an organic dye as the gain medium. The wide gain spectrum of available dyes, or mixtures of dyes, allows these lasers to be highly tunable, or to produce very short-duration pulses on the order of a few femtoseconds.

Although these tunable lasers are mainly known in their liquid form, researchers have also demonstrated narrow-linewidth tunable emission in dispersive oscillator configurations incorporating solid-state dye gain media. In their most prevalent form these solid state dye lasers use dye-doped polymers as laser media.

Free-electron lasers , or FELs, generate coherent, high power radiation that is widely tunable, currently ranging in wavelength from microwaves through terahertz radiation and infrared to the visible spectrum, to soft X-rays. They have the widest frequency range of any laser type. While FEL beams share the same optical traits as other lasers, such as coherent radiation, FEL operation is quite different.

Unlike gas, liquid, or solid-state lasers, which rely on bound atomic or molecular states, FELs use a relativistic electron beam as the lasing medium, hence the term free-electron. The pursuit of a high-quantum-energy laser using transitions between isomeric states of an atomic nucleus has been the subject of wide-ranging academic research since the early s.

Much of this is summarized in three review articles. While many scientists remain optimistic that a breakthrough is near, an operational gamma-ray laser is yet to be realized. In September , the BBC News reported that there was speculation about the possibility of using positronium annihilation to drive a very powerful gamma ray laser. David Cassidy of the University of California, Riverside proposed that a single such laser could be used to ignite a nuclear fusion reaction, replacing the banks of hundreds of lasers currently employed in inertial confinement fusion experiments.

Space-based X-ray lasers pumped by a nuclear explosion have also been proposed as antimissile weapons. Living cells have been used to produce laser light. The cells were then placed between two 20 micrometer wide mirrors, which acted as the laser cavity. When the cell was illuminated with blue light, it emitted intense, directed green laser light. Like astrophysical masers , irradiated planetary or stellar gases may amplify light producing a natural laser.

When lasers were invented in , they were called “a solution looking for a problem”. Fiber-optic communication using lasers is a key technology in modern communications, allowing services such as the Internet.

The first widely noticeable use of lasers was the supermarket barcode scanner , introduced in The laserdisc player, introduced in , was the first successful consumer product to include a laser but the compact disc player was the first laser-equipped device to become common, beginning in followed shortly by laser printers. Lasers have many uses in medicine, including laser surgery particularly eye surgery , laser healing photobiomodulation therapy , kidney stone treatment, ophthalmoscopy , and cosmetic skin treatments such as acne treatment, cellulite and striae reduction, and hair removal.

Lasers are used to treat cancer by shrinking or destroying tumors or precancerous growths. They are most commonly used to treat superficial cancers that are on the surface of the body or the lining of internal organs.