Array ( [0] => {{short description|Device which emits light via optical amplification}} [1] => {{other uses}} [2] => {{redirect-distinguish|Laser beam|LazarBeam|Lazer Beam}} [3] => {{pp-semi-indef}} [4] => {{Use mdy dates|date=June 2012}} [5] => {{Use American English|date=September 2016}} [6] => [[File:Guiding the Milky Way (potw2222a).jpg|thumb|upright=1.5|A telescope in the [[Very Large Telescope]] system producing four orange [[laser guide star]]s |alt=A telescope emitting four orange laser beams.]] [7] => [8] => A '''laser''' is a device that emits [[light]] through a process of [[optical amplification]] based on the [[stimulated emission]] of [[electromagnetic radiation]]. The word ''laser'' is an [[wiktionary:anacronym|anacronym]] that originated as an acronym for '''light amplification by stimulated emission of radiation'''.{{Cite book |last=Taylor |first=Nick |title=Laser: The Inventor, The Nobel Laureate, and The Thirty-Year Patent War |publisher=[[Simon & Schuster]] |year=2000 |isbn=978-0684835150 |page=[https://www.google.com/books/edition/Laser/Q7DaoWJyPjIC?&gbpv=1&pg=PA66&printsec=frontcover 66]}}{{Cite book |last1=Ross T. |first1=Adam |url=https://books.google.com/books?id=z1BRAAAAMAAJ |title=Proceedings of Laser Surgery: Advanced Characterization, Therapeutics, and Systems |last2=Becker G. |first2=Daniel |date=2001 |publisher=[[SPIE]] |isbn=978-0-8194-3922-2 |pages=396 |language=en}} The first laser was built in 1960 by [[Theodore Maiman]] at [[Hughes Research Laboratories]], based on theoretical work by [[Charles H. Townes]] and [[Arthur Leonard Schawlow]].{{Cite web |title=December 1958: Invention of the Laser |url=http://www.aps.org/publications/apsnews/200312/history.cfm|access-date=January 27, 2022 |website=aps.org |language=en|archive-date=December 10, 2021 |archive-url=https://web.archive.org/web/20211210153614/https://www.aps.org/publications/apsnews/200312/history.cfm |url-status=live}} [9] => [10] => A laser differs from other sources of light in that it emits light that is [[coherence (physics)|''coherent'']]. [[Spatial coherence]] allows a laser to be focused to a tight spot, enabling applications such as [[laser cutting]] and [[Photolithography#Light sources|lithography]]. It also allows a laser beam to stay narrow over great distances ([[collimated light|collimation]]), a feature used in applications such as [[laser pointer]]s and [[lidar]] (light detection and ranging). Lasers can also have high [[temporal coherence]], which permits them to emit light with a very narrow [[frequency spectrum]]. Alternatively, temporal coherence can be used to produce [[ultrashort pulse]]s of light with a broad spectrum but durations as short as a [[femtosecond]]. [11] => [12] => Lasers are used in [[optical disc drive]]s, [[laser printer]]s, [[barcode scanner]]s, [[DNA sequencer|DNA sequencing instruments]], [[fiber-optic communication|fiber-optic]], and [[free-space optical communication]], semiconducting chip manufacturing ([[photolithography]]), [[laser surgery]] and skin treatments, cutting and [[laser welding|welding]] materials, military and [[law enforcement]] devices for marking targets and [[Laser rangefinder|measuring range]] and speed, and in [[laser lighting display]]s for entertainment. Semiconductor lasers in the blue to [[Ultraviolet|near-UV]] have also been used in place of [[light-emitting diode]]s (LEDs) to excite [[fluorescence]] as a white light source; this permits a much smaller emitting area due to the much greater [[radiance]] of a laser and avoids the [[Light-emitting diode physics#Efficiency droop|droop]] suffered by LEDs; such devices are already used in some car [[headlamp]]s.{{Cite web | url=https://www.laserfocusworld.com/articles/print/volume-49/issue-11/world-news/semiconductor-sources-laser-plus-phosphor-emits-white-light-without-droop.html | title=Semiconductor Sources: Laser plus phosphor emits white light without droop | date=November 7, 2013 | access-date=February 4, 2019 | archive-date=June 13, 2016 | archive-url=https://web.archive.org/web/20160613090210/https://www.laserfocusworld.com/articles/print/volume-49/issue-11/world-news/semiconductor-sources-laser-plus-phosphor-emits-white-light-without-droop.html | url-status=live}}{{Cite web | url=https://www.laserfocusworld.com/articles/print/volume-53/issue-02/world-news/laser-lighting-white-light-lasers-challenge-leds-in-directional-lighting-applications.html | title=Laser Lighting: White-light lasers challenge LEDs in directional lighting applications | date=February 22, 2017 | access-date=February 4, 2019 | archive-date=February 7, 2019 | archive-url=https://web.archive.org/web/20190207015040/https://www.laserfocusworld.com/articles/print/volume-53/issue-02/world-news/laser-lighting-white-light-lasers-challenge-leds-in-directional-lighting-applications.html | url-status=live}}{{Cite web|url = https://auto.howstuffworks.com/laser-powered-headlight.htm|title = How Laser-powered Headlights Work|date = November 7, 2011|access-date = February 4, 2019|archive-date = November 16, 2011|archive-url = https://web.archive.org/web/20111116164353/https://auto.howstuffworks.com/laser-powered-headlight.htm|url-status = live}}{{Cite web | url=https://www.osram.com/am/specials/trends-in-automotive-lighting/laser-light-new-headlight-technology/index.jsp | title=Laser light for headlights: Latest trend in car lighting | OSRAM Automotive | access-date=February 4, 2019 | archive-date=February 7, 2019 | archive-url=https://web.archive.org/web/20190207015523/https://www.osram.com/am/specials/trends-in-automotive-lighting/laser-light-new-headlight-technology/index.jsp | url-status=live}} [13] => [14] => == Terminology == [15] => The first device using amplification by stimulated emission operated at [[microwave]] frequencies, and was called a ''[[maser]]'', for "microwave amplification by stimulated emission of radiation".{{Cite book |last=Heilbron |first=John L. |url=https://archive.org/details/oxfordcompaniont0000unse_s7n3 |title=The Oxford Companion to the History of Modern Science |date=2003-03-27 |publisher=[[Oxford University Press]] |isbn=978-0-19-974376-6 |pages=[https://archive.org/details/oxfordcompaniont0000unse_s7n3/page/446/mode/2up 447] |language=en |url-access=registration}} When similar [[Visible spectrum|optical]] devices were developed they were first known as ''optical masers'', until "microwave" was replaced by "light" in the acronym, to become ''laser''.{{Cite book |last=Bertolotti |first=Mario |url= |title=The History of the Laser |date=2004-10-01 |publisher=[[CRC Press]] |isbn=978-1-4200-3340-3 |pages=[https://www.google.com/books/edition/The_History_of_the_Laser/JObDnEtzMJUC?&gbpv=1&PA=215&printsec=frontcover 215], [https://www.google.com/books/edition/The_History_of_the_Laser/JObDnEtzMJUC?&gbpv=1&PA=218&printsec=frontcover 218]–[https://www.google.com/books/edition/The_History_of_the_Laser/JObDnEtzMJUC?&gbpv=1&PA=219&printsec=frontcover 219] |language=en}} [16] => [17] => Today, all such devices operating at frequencies higher than microwaves (approximately above 300 [[Hertz|GHz]]) are called lasers (e.g. ''infrared lasers'', ''ultraviolet lasers'', ''[[X-ray laser]]s'', ''[[gamma-ray laser]]s''), whereas devices operating at [[microwave]] or lower [[Radio frequency|radio frequencies]] are called masers.{{Cite book |last=McAulay |first=Alastair D. |url= |title=Military Laser Technology for Defense: Technology for Revolutionizing 21st Century Warfare |date=2011-05-31 |publisher=[[John Wiley & Sons]] |isbn=978-0-470-25560-5 |page=[https://www.google.com/books/edition/Military_Laser_Technology_for_Defense/6nFguMVUXAgC?&pg=PA127&printsec=frontcover 127] |language=en}}{{Cite book |last=Renk |first=Karl F. |url= |title=Basics of Laser Physics: For Students of Science and Engineering |date=2012-02-09 |publisher=[[Springer Science & Business Media]] |isbn=978-3-642-23565-8 |page=[https://www.google.com/books/edition/Basics_of_Laser_Physics/uN6RDgAAQBAJ?&gbpv=1&pg=PA4&printsec=frontcover 4] |language=en}} [18] => [19] => The [[back-formation|back-formed]] verb "[[wikt:en:lase#English|to lase]]" is frequently used in the field, meaning "to give off coherent light," especially about the [[Active laser medium|gain medium]] of a laser;{{Cite web |title=LASE |url=https://www.collinsdictionary.com/dictionary/english/lase# |access-date=January 6, 2024 |website=[[Collins_English_Dictionary#CollinsDictionary.com|Collins Dictionary]]}} when a laser is operating it is said to be "[[wikt:en:lasing#English|lasing]]".{{Cite web |title=LASING |url=https://www.collinsdictionary.com/dictionary/english/lasing# |access-date=January 6, 2024 |website=[[Collins_English_Dictionary#CollinsDictionary.com|Collins Dictionary]]}} The terms ''laser'' and ''maser'' are also used for naturally occurring coherent emissions, as in ''[[astrophysical maser]]'' and ''[[atom laser]]''.{{cite journal |last1=Strelnitski |first1=Vladimir |year=1997 |title=Masers, Lasers and the Interstellar Medium |journal=Astrophysics and Space Science |volume=252 |pages=279–287 |bibcode=1997Ap&SS.252..279S |doi=10.1023/A:1000892300429 |s2cid=115181195}} [20] => [21] => A laser that produces light by itself is technically an optical oscillator rather than an [[optical amplifier]] as suggested by the acronym.{{Cite book |last1=Al-Amri |first1=Mohammad D. |url= |title=Optics in Our Time |last2=El-Gomati |first2=Mohamed |last3=Zubairy |first3=M. Suhail |date=2016-12-12 |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-3-319-31903-2 |page=[https://www.google.com/books/edition/Optics_in_Our_Time/GtlCDwAAQBAJ?&gbpv=1&pg=PA76&printsec=frontcover 76] |language=en}} It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation", would have been more correct.{{cite book |last1=Chu |first1=Steven |author-link=Steven Chu |last2=Townes |first2=Charles |author-link2=Charles Hard Townes |editor=Edward P. Lazear |title=Biographical Memoirs |year=2003 |volume=83 |publisher=National Academy of Sciences |isbn=978-0-309-08699-8 |page=202 |chapter=Arthur Schawlow |url=http://www.nap.edu/openbook/030908699X/html/202.html }} With the widespread use of the original acronym as a common noun, optical amplifiers have come to be referred to as ''laser amplifiers''.{{Cite book |last=Hecht |first=Jeff |url= |title=Understanding Lasers: An Entry-Level Guide |date=2018-12-27 |publisher=[[John Wiley & Sons]] |isbn=978-1-119-31064-8 |page=[https://www.google.com/books/edition/Understanding_Lasers/2nJ6DwAAQBAJ?&gbpv=1&pg=PA201&printsec=frontcover 201] |language=en}} [22] => [23] => == Fundamentals == [24] => {{more citations needed section|date=October 2023}} [25] => [[File:Green Laser.jpg|thumb|right|A laser normally produces a very narrow beam of light in a single wavelength, in this case, green.]] [26] => Modern physics describes light and other forms of [[electromagnetic radiation]] as the group behavior of [[fundamental particle]]s known as ''[[photon]]s''. Photons are released and absorbed through [[electromagnetism|electromagnetic]] interactions with other fundamental particles that carry [[electric charge]]. A common way to release photons is to heat an object; some of the [[thermal energy]] being applied to the object will cause the [[molecule]]s and [[electron]]s within the object to gain energy, which is then lost through [[thermal radiation]], that we see as light. This is the process that causes a candle flame to give off light. [27] => [28] => Thermal radiation is a random process, and thus the photons emitted have a range of different [[wavelength]]s, travel in different directions, and are released at different times. The energy within the object is not random, however: it is stored by atoms and molecules in "[[excited state]]s", which release photons with distinct wavelengths. This gives rise to the science of [[spectroscopy]], which allows materials to be determined through the specific wavelengths that they emit. [29] => [30] => The underlying physical process creating photons in a laser is the same as in thermal radiation, but the actual emission is not the result of random thermal processes. Instead, the release of a photon is triggered by the nearby passage of another photon. This is called [[stimulated emission]]. For this process to work, the passing photon must be similar in energy, and thus wavelength, to the one that could be released by the atom or molecule, and the atom or molecule must be in the suitable excited state. [31] => [32] => The photon that is emitted by stimulated emission is identical to the photon that triggered its emission, and both photons can go on to trigger stimulated emission in other atoms, creating the possibility of a [[chain reaction]]. For this to happen, many of the atoms or molecules must be in the proper excited state so that the photons can trigger them. In most materials, atoms or molecules drop out of excited states fairly rapidly, making it difficult or impossible to produce a chain reaction. The materials chosen for lasers are the ones that have [[Metastability|metastable states]], which stay excited for a relatively long time. In [[Laser science|laser physics]], such a material is called an [[active laser medium]]. Combined with an energy source that continues to "pump" energy into the material, this makes it possible to have enough atoms or molecules in an excited state for a chain reaction to develop. [33] => [34] => Lasers are distinguished from other light sources by their [[coherence (physics)|coherence]]. Spatial (or transverse) coherence is typically expressed through the output being a narrow beam, which is [[Gaussian beam|diffraction-limited]]. Laser beams can be focused to very tiny spots, achieving a very high [[irradiance]], or they can have a very low divergence to concentrate their power at a great distance. Temporal (or longitudinal) coherence implies a [[Polarization (waves)|polarized]] wave at a single frequency, whose phase is correlated over a relatively great distance (the [[coherence length]]) along the beam.''Conceptual physics'', Paul Hewitt, 2002{{Page missing|date=January 2024}} A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and [[phase (waves)|phase]] that vary randomly with respect to time and position, thus having a short coherence length. [35] => [36] => Lasers are characterized according to their [[wavelength]] in a [[vacuum]]. Most "single wavelength" lasers produce radiation in several ''modes'' with slightly different wavelengths. Although temporal coherence implies some degree of [[Monochromatic radiation|monochromaticity]], some lasers emit a broad spectrum of light or emit different wavelengths of light simultaneously. Certain lasers are not single spatial mode and have light beams that [[Beam divergence|diverge]] more than is required by the [[diffraction limit]]. All such devices are classified as "lasers" based on the method of producing light by stimulated emission. Lasers are employed where light of the required spatial or temporal coherence can not be produced using simpler technologies. [37] => [38] => == Design == [39] => {{Main|Laser construction}}{{more citations needed section|date=October 2023}}[[File:Laser.svg|thumb|Components of a typical laser: {{ordered list |Gain medium |Laser pumping energy |High reflector |[[Output coupler]] |Laser beam}}]] [40] => [41] => A laser consists of a [[Active laser medium|gain medium]], a mechanism to energize it, and something to provide optical [[feedback]].{{cite book |last=Siegman |first=Anthony E. |url=https://archive.org/details/lasers0000sieg |title=Lasers |publisher=University Science Books |year=1986 |isbn=978-0-935702-11-8 |page=[https://archive.org/details/lasers0000sieg/page/2 2] |author-link=Anthony E. Siegman |url-access=registration}} The gain medium is a material with properties that allow it to [[optical amplifier|amplify]] light by way of stimulated emission. Light of a specific wavelength that passes through the gain medium is amplified (power increases). Feedback enables stimulated emission to amplify predominantly the optical frequency at the peak of the gain-frequency curve. As stimulated emission grows, eventually one frequency dominates over all others, meaning that a coherent beam has been formed.{{cite book |last1=Pearsall |first1=Thomas |title=Quantum Photonics, 2nd edition |publisher=Springer |date=2020 |doi=10.1007/978-3-030-47325-9|url=https://www.springer.com/us/book/9783030473242 |isbn=978-3-030-47324-2 |series=Graduate Texts in Physics |s2cid=240934073 |access-date=February 23, 2021 |archive-date=February 25, 2021 |archive-url=https://web.archive.org/web/20210225061649/https://www.springer.com/us/book/9783030473242 |url-status=live}}{{Page missing|date=January 2024}} The process of stimulated emission is analogous to that of an audio oscillator with positive feedback which can occur, for example, when the speaker in a public-address system is placed in proximity to the microphone. The screech one hears is audio oscillation at the peak of the gain-frequency curve for the amplifier.{{cite book |last1=Pearsall |first1=Thomas |title=Photonics Essentials, 2nd edition |publisher=McGraw-Hill |date=2010 |url=https://www.mheducation.com/highered/product/photonics-essentials-second-edition-pearsall/9780071629355.html|isbn=978-0-07-162935-5 |access-date=February 23, 2021 |archive-date=August 17, 2021 |archive-url=https://web.archive.org/web/20210817005021/https://www.mheducation.com/highered/product/photonics-essentials-second-edition-pearsall/9780071629355.html|url-status=dead}}{{Page missing|date=January 2024}} [42] => [43] => For the gain medium to amplify light, it needs to be supplied with energy in a process called [[laser pumping|pumping]]. The energy is typically supplied as an electric current or as light at a different wavelength. Pump light may be provided by a [[Xenon flash lamp|flash lamp]] or by another laser. [44] => [45] => The most common type of laser uses feedback from an [[optical cavity]]{{mdash}}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 mirror|curved]]), the light coming out of the laser may spread out or form a narrow [[light beam|beam]]. In analogy to [[electronic oscillator]]s, this device is sometimes called a ''laser oscillator''. [46] => [47] => Most practical lasers contain additional elements that affect the properties of the emitted light, such as the polarization, wavelength, and shape of the beam.{{citation needed|date=February 2023}} [48] => [49] => == Laser physics == [50] => {{more citations needed section|date=May 2017}} [51] => {{See also|Laser science}} [52] => [53] => [[Electron]]s and how they interact with [[electromagnetic field]]s are important in our understanding of [[chemistry]] and [[physics]]. [54] => [55] => === Stimulated emission === [56] => {{Main|Stimulated emission}} [57] => [58] => [[File:Laser, quantum principle.ogv|thumb|upright=1.5|Animation explaining stimulated emission and the laser principle]] [59] => [60] => In the [[Classical electromagnetism|classical view]], the energy of an electron orbiting an atomic nucleus is larger for orbits further from the [[atomic nucleus|nucleus]] of an [[atom]]. However, quantum mechanical effects force electrons to take on discrete positions in [[Atomic orbital|orbitals]]. Thus, electrons are found in specific energy levels of an atom, two of which are shown below: [61] => [62] => [[File:Stimulated Emission.svg|frameless|center|upright=2]] [63] => [64] => An electron in an atom can absorb energy from light ([[photon]]s) or heat ([[phonon]]s) only if there is a transition between energy levels that match the energy carried by the photon or phonon. For light, this means that any given transition will only [[Absorption (electromagnetic radiation)|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. [65] => [66] => When an electron is [[excited state|excited]] from one state to that at a higher energy level with energy difference ΔE, it will not stay that way forever. Eventually, a photon will be spontaneously created from the vacuum having energy ΔE. Conserving energy, the electron transitions to a lower energy level that 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 a random direction, but its wavelength matches the absorption wavelength of the transition. This is the mechanism of [[fluorescence]] and [[thermal emission]]. [67] => [68] => 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. [69] => [70] => === Gain medium and cavity === [71] => [[File:Laser DSC09088.JPG|thumb|A [[helium–neon laser]] demonstration. The glow running through the center of the tube is an electric discharge. This glowing plasma is the [[active laser medium|gain medium]] for the laser. The laser produces a tiny, intense spot on the screen to the right. The center of the spot appears white because the image is [[overexposure|overexposed]] there.]] [72] => [[File:Helium neon laser spectrum.svg|thumb|Spectrum of a helium–neon laser. The actual bandwidth is much narrower than shown; the spectrum is limited by the measuring apparatus.]] [73] => [74] => 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 that have been excited into such a state using an outside light source, or an electrical field that supplies energy for atoms to absorb and be transformed into their excited states. [75] => [76] => 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 of matter|state]]: gas, liquid, solid, or [[plasma (physics)|plasma]]. The gain medium absorbs pump energy, which raises some electrons into higher energy ("[[excited state|excited]]") [[quantum state]]s. 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.{{cite book |first = Anthony E. |last=Siegman |year=1986 |title=Lasers |url = https://archive.org/details/lasers0000sieg |url-access = registration |publisher=University Science Books |isbn= 978-0-935702-11-8 |page=[https://archive.org/details/lasers0000sieg/page/4 4]}} [77] => [78] => For lasing media with extremely high gain, so-called [[superluminescence]], light can 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]]),{{cite book [79] => |title=Light and Its Uses [80] => |chapter=Nitrogen Laser [81] => |work=Scientific American [82] => |date=June 1974 [83] => |isbn=978-0-7167-1185-8 [84] => |pages=[https://archive.org/details/lightitsusesmaki0000unse/page/40 40–43] [85] => |ref=Light and Its Uses [86] => |chapter-url=https://archive.org/details/lightitsusesmaki0000unse/page/40 [87] => |last1=Walker [88] => |first1=Jearl [89] => |publisher=W. H. Freeman [90] => }} 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 as a high-gain optical amplifier that amplifies its spontaneous emission. The same mechanism describes so-called [[astrophysical maser]]s/lasers. [91] => [92] => 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]]. [93] => The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting 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. [94] => If the gain (amplification) in the medium is larger than the resonator losses, then the power of the recirculating light can rise [[exponential growth|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. [95] => [96] => === The light emitted === [97] => [98] => [[File:Lasers.JPG|thumb|Red (660 & 635 nm), green (532 & 520 nm), and blue-violet (445 & 405 nm) lasers]]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 (waves)|phase]] of the emitted light is 90 degrees in lead of the stimulating light.{{cite journal | last1 = Pollnau | first1 = M. | year = 2018 | title = Phase aspect in photon emission and absorption | journal = Optica | volume = 5 | issue = 4 | pages = 465–474 | doi = 10.1364/OPTICA.5.000465 | bibcode = 2018Optic...5..465P | url = https://www.osapublishing.org/DirectPDFAccess/C50A8E4B-9698-1EAB-90F88B72D53AEB42_385547/optica-5-4-465.pdf?da=1&id=385547&seq=0&mobile=no | doi-access = free | access-date = June 28, 2020 | archive-date = February 8, 2023 | archive-url = https://web.archive.org/web/20230208064609/https://opg.optica.org/static307.htm?da=1&id=385547&seq=0&mobile=no | url-status = live}} This, combined with the filtering effect of the optical resonator gives laser light its characteristic coherence, and may give it uniform polarization and monochromaticity, depending on the resonator's design. The fundamental [[laser linewidth]]{{cite journal | last1 = Pollnau | first1 = M. | last2 = Eichhorn | first2 = M. | year = 2020 | title = Spectral coherence, Part I: Passive resonator linewidth, fundamental laser linewidth, and Schawlow-Townes approximation | journal = Progress in Quantum Electronics | volume = 72 | pages = 100255 | doi = 10.1016/j.pquantelec.2020.100255 | bibcode = 2020PQE....7200255P | doi-access = free}} 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. [99] => [100] => In 1963, [[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]].{{cite journal | last1 = Glauber | first1 = R.J. | year = 1963 | title = Coherent and incoherent states of the radiation field | journal = Phys. Rev. | volume = 131 | issue = 6 | pages = 2766–2788 | doi = 10.1103/PhysRev.131.2766 | bibcode = 1963PhRv..131.2766G | url = http://conf.kias.re.kr/~brane/wc2006/lec_note/Glauber-2.pdf | access-date = February 23, 2021 | archive-date = May 8, 2021 | archive-url = https://web.archive.org/web/20210508173506/http://conf.kias.re.kr/~brane/wc2006/lec_note/Glauber-2.pdf | url-status = live}} A coherent beam of light is formed by single-frequency quantum photon states distributed according to a [[Poisson distribution]]. As a result, the arrival rate of photons in a laser beam is described by Poisson statistics.{{Page missing|date=January 2024}} [101] => [102] => 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 mode]]s often approximated using [[Hermite polynomials|Hermite]]–[[Gaussian function|Gaussian]] or [[Laguerre polynomials|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.{{cite journal | last1 = Karman | first1 = G.P. | last2 = McDonald | first2 = G.S. | last3 = New | first3 = G.H.C. | last4 = Woerdman | first4 = J.P. | author-link4 = Han Woerdman | title = Laser Optics: Fractal modes in unstable resonators | journal = Nature | volume = 402 | issue = 6758| page = 138 | doi=10.1038/45960| bibcode = 1999Natur.402..138K | date = November 1999 | s2cid = 205046813 | doi-access = free}} Specialized optical systems can produce more complex beam geometries, such as [[Bessel beam]]s and [[optical vortex]]es. [103] => [104] => Near the "waist" (or [[focus (optics)|focal region]]) of a laser beam, it is highly ''[[collimated light|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 that 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 500 kilometers when shone on the Moon (from the distance of the earth). On the other hand, the light from a [[semiconductor laser]] typically exits the tiny crystal with a large divergence: up to 50°. However even such a divergent beam can be transformed into a similarly collimated beam employing a [[lens (optics)|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. [105] => [106] => A [[laser beam profiler]] is used to measure the intensity profile, width, and divergence of laser beams. [107] => [108] => [[Diffuse reflection]] of a laser beam from a matte surface produces a [[speckle pattern]] with interesting properties. [109] => [110] => === Quantum vs. classical emission processes === [111] => [112] => 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|date=June 2021}} that was predicted by [[Albert Einstein]], who derived the relationship between the [[Spontaneous emission#Rate of spontaneous emission|A coefficient]] describing spontaneous emission and the [[Stimulated emission#Mathematical model|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]]. [113] => [114] => == Modes of operation == [115] => {{more citations needed|section|date=February 2023}} [116] => [[File:Moon clementine lidar.jpg|thumb|[[Lidar]] measurements of lunar topography made by [[Clementine (spacecraft)|Clementine]] mission]] [117] => [[File:Laserlink hss46.jpg|thumb|Laserlink [[Point-to-point (telecommunications)|point to point]] optical wireless network]] [118] => [[File:MESSENGER - MLA.jpg|thumb|Mercury Laser Altimeter (MLA) of the [[MESSENGER]] spacecraft]] [119] => [120] => 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 to create pulses of light. When the modulation rate is on time scales much slower than the [[Q factor#Optical systems|cavity lifetime]] and the 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 into that category. [121] => [122] => === Continuous-wave operation === [123] => {{^| [[Continuous wave laser]] and [[Continuous-wave laser]] redirect here}}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 lase in several longitudinal modes at the same time, and beats between the slightly different optical frequencies of those oscillations will produce amplitude variations on time scales shorter than the round-trip time (the reciprocal of the [[Free spectral range#Fabry–Pérot interferometer|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 longer periods, with the very high-frequency power variations having little or no impact on the intended application. (However, the term is not applied to [[Mode locking|mode-locked]] lasers, where the ''intention'' is to create very short pulses at the rate of the round-trip time.) [124] => [125] => 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 destroying the laser by producing excessive heat. Such lasers cannot be run in CW mode. [126] => [127] => === Pulsed operation === [128] => {{Main|Pulsed laser}} [129] => [130] => The pulsed operation of lasers refers to any laser not classified as a 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 many different motivations. Some lasers are pulsed simply because they cannot be run in [[#Continuous wave operation|continuous]] mode. [131] => [132] => 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 between pulses. In [[laser ablation]], for example, a small volume of material at the surface of a workpiece 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. [133] => [134] => Other applications rely on the peak pulse power (rather than the energy in the pulse), especially 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]]. [135] => [136] => 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. The lasing medium in some ''dye lasers'' and ''vibronic solid-state lasers'' produces optical gain over a wide bandwidth, making a laser possible that can thus generate pulses of light as short as a few [[femtoseconds]] (10−15 s). [137] => [138] => ==== Q-switching ==== [139] => {{Main|Q-switching}} [140] => [141] => 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. [142] => [143] => ==== Mode locking ==== [144] => {{Main|Mode locking}} [145] => [146] => A mode-locked laser is capable of emitting extremely short pulses on the order of tens of [[picosecond]]s 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 uncertainty principle|Fourier limit]] (also known as energy–time [[Uncertainty principle|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 laser|Ti:sapphire]]), which has a very wide gain bandwidth and can thus produce pulses of only a few femtoseconds duration. [147] => [148] => 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 [[nonlinear optics|nonlinearity]] in optical materials (e.g. in [[second-harmonic generation]], [[parametric down-conversion]], [[optical parametric oscillator]]s and the like). 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 [[Envelope (waves)|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. [149] => [150] => ==== Pulsed pumping ==== [151] => 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 that 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. [152] => [153] => == History == [154] => [155] => === Foundations === [156] => [157] => In 1917, [[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.{{cite journal |last=Einstein |first=A |title=Zur Quantentheorie der Strahlung |journal=Physikalische Zeitschrift |year=1917 |volume=18 |pages=121–128 |bibcode = 1917PhyZ...18..121E }} In 1928, [[Rudolf W. Ladenburg]] confirmed the existence of the phenomena of stimulated emission and negative absorption.Steen, W.M. "Laser Materials Processing", 2nd Ed. 1998.{{Page missing|date=January 2024}} In 1939, [[Valentin A. Fabrikant]] predicted the use of stimulated emission to amplify "short" waves.{{cite web |url=http://wwwold.unimib.it/ateneo/presentazione/direzione_ammva/prevenzione_protezione/Semin_sicur_laser.ppt |title=Il rischio da laser: cosa è e come affrontarlo; analisi di un problema non così lontano da noi |trans-title=The risk from laser: what it is and what it is like facing it; analysis of a problem which is thus not far away from us |series=Programma Corso di Formazione Obbligatorio |year=2004 |first=Dimitri |last=Batani |format=Powerpoint |access-date=January 1, 2007 |website=wwwold.unimib.it |publisher=University of Milano-Bicocca |language=it |archive-url=https://web.archive.org/web/20070614115935/http://wwwold.unimib.it/ateneo/presentazione/direzione_ammva/prevenzione_protezione/Semin_sicur_laser.ppt |archive-date=June 14, 2007 |page=12}} In 1947, [[Willis E. Lamb]] and R.{{nbsp}}C.{{nbsp}}Retherford found apparent stimulated emission in hydrogen spectra and effected the first demonstration of stimulated emission.{{Page missing|date=January 2024}} In 1950, [[Alfred Kastler]] (Nobel Prize for Physics 1966) proposed the method of [[optical pumping]], which was experimentally demonstrated two years later by Brossel, Kastler, and Winter.[http://nobelprize.org/nobel_prizes/physics/laureates/1966/press.html The Nobel Prize in Physics 1966] {{Webarchive |url=https://web.archive.org/web/20110604225702/http://nobelprize.org/nobel_prizes/physics/laureates/1966/press.html |date=June 4, 2011 }} Presentation Speech by Professor Ivar Waller. Retrieved January 1, 2007. [158] => [159] => === Maser === [160] => {{Main|Maser}} [161] => [162] => [[File:Aleksandr Prokhorov.jpg|thumb|right|[[Aleksandr Mikhailovich Prokhorov|Aleksandr Prokhorov]]]] [163] => [164] => In 1951, [[Joseph Weber]] submitted a paper on using stimulated emissions to make a microwave amplifier to the June 1952 Institute of Radio Engineers Vacuum Tube Research Conference at [[Ottawa]], Ontario, Canada.{{cite web| url=https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4941| title=American Institute of Physics Oral History Interview with Joseph Weber| date=2015-05-04| access-date=March 16, 2016| archive-date=March 8, 2016| archive-url=https://web.archive.org/web/20160308061348/https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4941 |url-status=live}} After this presentation, [[RCA]] asked Weber to give a seminar on this idea, and [[Charles H. Townes]] asked him for a copy of the paper.{{cite book |last=Bertolotti |first=Mario |year=2015 |title=Masers and Lasers: An Historical Approach |publisher=CRC Press |pages=89–91 |isbn=978-1-4822-1780-3 |edition=2nd |url=https://books.google.com/books?id=4i_OBgAAQBAJ |access-date=March 15, 2016}} [165] => [166] => [[File:Charles Townes.jpg|thumb|right|[[Charles H. Townes]]]] [167] => [168] => In 1953, Charles H. Townes and graduate students [[James P. 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.{{cite web |url=https://hobarts.com/guide-to-lasers |title=Guide to Lasers |website=Hobarts |access-date=24 April 2017 |archive-date=April 24, 2019 |archive-url=https://web.archive.org/web/20190424211422/https://hobarts.com/guide-to-lasers |url-status=live}} Meanwhile, in the Soviet Union, [[Nikolay Basov]] and [[Aleksandr Mikhailovich Prokhorov|Aleksandr Prokhorov]] were independently working on the [[Quantum harmonic oscillator|quantum oscillator]] and solved the problem of continuous-output systems by using more than two energy levels. These gain media could release [[stimulated emission]]s between an excited state and a lower excited state, not the ground state, facilitating the maintenance of a [[population inversion]]. In 1955, 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. [169] => [170] => Townes reports that several eminent physicists{{mdash}}among them [[Niels Bohr]], [[John von Neumann]], and [[Llewellyn Thomas]]{{mdash}}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, Charles H. (1999). [https://books.google.com/books?id=VrbD41GGeJYC&dq=%22niels+bohr%22+rabi+kusch+von+neumann+laser&pg=PA69 ''How the Laser Happened: Adventures of a Scientist''], [[Oxford University Press]], {{ISBN|978-0-19-512268-8}}, pp. 69–70. 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 construction of oscillators and amplifiers based on the maser–laser principle". [171] => [172] => === Laser === [173] => [174] => In April 1957, Japanese engineer [[Jun-ichi Nishizawa]] proposed the concept of a "[[semiconductor laser|semiconductor optical maser]]" in a patent application.{{cite journal |title=Extension of frequencies from maser to laser |first=Jun-ichi |last=Nishizawa |journal=Proc Jpn Acad Ser B Phys Biol Sci |date=Dec 2009 |volume=85 |issue=10 |pages=454–465 |doi=10.2183/pjab.85.454|pmid=20009378 |pmc=3621550 |bibcode=2009PJAB...85..454N |doi-access=free}} [175] => [176] => {{external media | float = right | headerimage= | audio1 = [https://www.sciencehistory.org/distillations/podcast/the-man-the-myth-the-laser "The Man, the Myth, the Laser"], ''Distillations'' Podcast, [[Science History Institute]]}} [177] => [178] => That same year, Charles H. Townes and Arthur Leonard Schawlow, then at [[Bell Labs]], began a serious study of infrared "optical masers". As ideas developed, they abandoned [[infrared]] radiation to instead concentrate on [[visible light]]. In 1958, 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 1958.{{cite journal |last1=Schawlow |first1=Arthur |last2=Townes |first2=Charles |title=Infrared and Optical Masers |year=1958 |doi=10.1103/PhysRev.112.1940 |journal=Physical Review |volume=112 |issue=6 |pages=1940–1949|bibcode = 1958PhRv..112.1940S |doi-access=free}} [179] => [180] => [[File:Gould notebook 001.jpg|thumb|right|'''LASER notebook:''' First page of the notebook wherein [[Gordon Gould]] coined the acronym LASER, and described the elements required to construct one. Manuscript text: "Some rough calculations on the feasibility / of a LASER: Light Amplification by Stimulated / Emission of Radiation. / [181] => Conceive a tube terminated by optically flat / [Sketch of a tube] / partially reflecting parallel mirrors..."]] [182] => [183] => Simultaneously, [[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 (electromagnetic radiation)|emission]], as a general subject; afterward, in November 1957, Gould noted his ideas for a "laser", including using an open [[resonator]] (later an essential laser-device component). Moreover, in 1958, 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. [184] => [185] => At a conference in 1959, Gordon Gould first published the acronym "LASER" in the paper ''The LASER, Light Amplification by Stimulated Emission of Radiation''.{{cite book |last=Gould |first= R. Gordon |author-link=Gordon Gould |year=1959 |chapter=The LASER, Light Amplification by Stimulated Emission of Radiation |editor= Franken, P.A. |editor2=Sands R.H.| title = The Ann Arbor Conference on Optical Pumping, the University of Michigan, 15 June through 18 June 1959 |page=128 |oclc=02460155}} Gould's intention was that different "-ASER" acronyms should be used for different parts of the spectrum: "XASER" for x-rays, "UVASER" for ultraviolet, etc. "LASER" ended up becoming the generic term for non-microwave devices, although "RASER" was briefly popular for denoting radio-frequency-emitting devices. [186] => [187] => Gould's notes included possible applications for a laser, such as [[Spectroscopy|spectrometry]], [[interferometry]], [[radar]], and [[nuclear fusion]]. He continued developing the idea and filed a [[patent application]] in April 1959. The [[United States Patent and Trademark Office]] (USPTO) denied his application, and awarded a patent to [[Bell Labs]], in 1960. That provoked a twenty-eight-year [[lawsuit]], featuring scientific prestige and money as the stakes. Gould won his first minor patent in 1977, yet it was not until 1987 that he won the first significant patent lawsuit victory when a Federal judge ordered the USPTO 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.Joan Lisa Bromberg, ''The Laser in America, 1950–1970'' (1991), pp. 74–77 [http://www.aip.org/history/exhibits/laser/sections/whoinvented.html online] {{Webarchive|url=https://web.archive.org/web/20140528023745/http://www.aip.org/history/exhibits/laser/sections/whoinvented.html |date=May 28, 2014}} [188] => [189] => On May 16, 1960, Theodore H. Maiman operated the first functioning laser{{cite journal |last=Maiman |first=T. H. |author-link=Theodore Harold Maiman |year=1960 |title=Stimulated optical radiation in ruby |journal=Nature |volume=187 |issue=4736 |pages=493–494 |doi=10.1038/187493a0 |bibcode = 1960Natur.187..493M |s2cid=4224209 }}{{cite web |access-date=May 15, 2008|url=http://www.press.uchicago.edu/Misc/Chicago/284158_townes.html |title=The first laser |publisher=[[University of Chicago]] |last=Townes |first=Charles Hard |author-link=Charles H. Townes |archive-date=April 4, 2004 |archive-url=https://web.archive.org/web/20040404035245/http://www.press.uchicago.edu/Misc/Chicago/284158_townes.html |url-status=live}} at [[Hughes Research Laboratories]], Malibu, California, ahead of several research teams, including those of Townes, at [[Columbia University]], [[Arthur L. Schawlow]], at [[Bell Labs]],{{cite book |last=Hecht |first=Jeff |year=2005 |title=Beam: The Race to Make the Laser |publisher=Oxford University Press |isbn=978-0-19-514210-5}}{{Page missing|date=January 2024}} and Gould, at the TRG (Technical Research Group) company. Maiman's functional laser used a [[flashlamp]]-pumped synthetic [[ruby]] [[crystal]] to produce red laser light at 694 nanometers wavelength. The device was only capable of pulsed operation, due to its three-level pumping design scheme. Later that year, the [[Iran]]ian physicist [[Ali Javan]], and [[William R. Bennett Jr.]], and [[Donald R. Herriott]], constructed the first [[gas laser]], using [[helium]] and [[neon]] that was capable of continuous operation in the infrared (U.S. Patent 3,149,290); later, Javan received the [[Albert Einstein World Award of Science]] in 1993. In 1962, [[Robert N. Hall]] demonstrated the first [[semiconductor laser]], which was made of [[gallium arsenide]] and emitted in the [[near-infrared]] band of the spectrum at 850 nm. Later that year, [[Nick Holonyak Jr.]] demonstrated the first semiconductor laser with a visible emission. This first semiconductor laser could only be used in pulsed-beam operation, and when cooled to [[liquid nitrogen]] temperatures (77 K). In 1970, [[Zhores Ivanovich Alferov|Zhores Alferov]], in the USSR, and Izuo Hayashi and Morton Panish of Bell Labs also independently developed room-temperature, continual-operation diode lasers, using the [[heterojunction]] structure. [190] => [191] => === Recent innovations === [192] => [[File:History of laser intensity.svg|thumb|Graph showing the history of maximum laser pulse intensity since 1960]] [193] => [194] => 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: [195] => * new wavelength bands [196] => * maximum average output power [197] => * maximum peak pulse [[energy]] [198] => * maximum peak pulse [[power (physics)|power]] [199] => * minimum output pulse duration [200] => * minimum linewidth [201] => * maximum power efficiency [202] => * minimum cost [203] => and this research continues to this day. [204] => [205] => In 2015, 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 191 nm.{{Cite web |url=https://www.popsci.com/scientists-have-finally-made-white-laser/ |title=For The First Time, A Laser That Shines Pure White |website=Popular Science |date=March 18, 2019 |access-date=December 16, 2019 |archive-date=December 16, 2019 |archive-url=https://web.archive.org/web/20191216085708/https://www.popsci.com/scientists-have-finally-made-white-laser/ |url-status=live}}{{Cite web |url=https://phys.org/news/2015-07-world-white-lasers.html |title=Researchers demonstrate the world's first white lasers |website=phys.org |access-date=December 16, 2019 |archive-date=December 16, 2019 |archive-url=https://web.archive.org/web/20191216085720/https://phys.org/news/2015-07-world-white-lasers.html |url-status=live}}{{Cite web |url=https://gizmodo.com/scientists-finally-created-a-white-laser-and-it-could-l-1721027962/amp |title=Scientists Finally Created a White Laser—and It Could Light Your Home |website=gizmodo.com |date=July 30, 2015 |access-date=December 16, 2019 |archive-date=December 16, 2019 |archive-url=https://web.archive.org/web/20191216085712/https://gizmodo.com/scientists-finally-created-a-white-laser-and-it-could-l-1721027962/amp |url-status=live}} [206] => [207] => In 2017, researchers at the [[Delft University of Technology]] demonstrated an [[Josephson effect#The AC Josephson effect|AC Josephson junction]] microwave laser.{{cite web |title=Researchers demonstrate new type of laser |url=https://phys.org/news/2017-03-laser.html |website=Phys.org |access-date=4 March 2017 |archive-date=March 3, 2017 |archive-url=https://web.archive.org/web/20170303164343/https://phys.org/news/2017-03-laser.html |url-status=live}} Since the laser operates in the superconducting regime, it is more stable than other semiconductor-based lasers. The device has the potential for applications in [[quantum computing]].{{cite journal |last1=Cassidy|first1=M. C. |last2=Bruno |first2=A. |last3=Rubbert |first3=S. |last4=Irfan |first4=M. |last5=Kammhuber |first5=J. |last6=Schouten |first6=R.N. |last7=Akhmerov |first7=A.R. |last8=Kouwenhoven |first8=L.P. |title=Demonstration of an ac Josephson junction laser |journal=Science |date=March 2, 2017 |volume=355 |issue=6328 |pages=939–942 |doi=10.1126/science.aah6640 |pmid=28254938 |arxiv=1703.05404 |bibcode=2017Sci...355..939C |s2cid=1364541}} In 2017, researchers at the [[Technical University of Munich]] demonstrated the smallest [[mode locking]] laser capable of emitting pairs of phase-locked picosecond laser pulses with a repetition frequency up to 200 GHz.{{cite journal|title=Long-term mutual phase locking of picosecond pulse pairs generated by a semiconductor nanowire laser |first1=B. |last1=Mayer |first2=A. |last2=Regler |first3=S. |last3=Sterzl |first4=T. |last4=Stettner |first5=G. |last5=Koblmüller |first6=M. |last6=Kaniber |first7=B. |last7=Lingnau |first8=K. |last8=Lüdge |first9=J.J. |last9=Finley |date=May 23, 2017 |journal=Nature Communications |volume=8 |pages=15521 |doi=10.1038/ncomms15521 |pmid=28534489 |pmc=5457509 |arxiv=1603.02169 |bibcode=2017NatCo...815521M}} [208] => [209] => In 2017, researchers from the [[Physikalisch-Technische Bundesanstalt]] (PTB), together with US researchers from [[JILA]], a joint institute of the National Institute of Standards and Technology (NIST) and the [[University of Colorado Boulder]], established a new world record by developing an erbium-doped fiber laser with a linewidth of only 10{{nbsp}}millihertz.{{cite press release |author=Erika Schow |url=http://www.ptb.de/cms/en/presseaktuelles/journalisten/news-press-releases/press-release.html |title=The Physikalisch-Technische Bundesanstalt has developed a laser with a linewidth of only 10 mHz |date=June 29, 2017 |url-status=dead |archive-url=https://web.archive.org/web/20170703235028/http://www.ptb.de/cms/en/presseaktuelles/journalisten/news-press-releases/press-release.html |archive-date=2017-07-03}}{{cite journal |title=1.5 μm Lasers with Sub-10 mHz Linewidth |first1=D.G. |last1=Matei |first2=T. |last2=Legero |first3=S. |last3=Häfner |first4=C. |last4=Grebing |first5=R. |last5=Weyrich |first6=W. |last6=Zhang |first7=L. |last7=Sonderhouse |first8=J.M. |last8=Robinson |first9=J. |last9=Ye |display-authors=3 |journal=Phys. Rev. Lett. |volume=118 |page=263202 |issue=26 |date=30 June 2017 |doi=10.1103/PhysRevLett.118.263202 |pmid=28707932 |arxiv=1702.04669 |bibcode=2017PhRvL.118z3202M |s2cid=206293342}} [210] => [211] => == Types and operating principles == [212] => {{Further|List of laser types}} [213] => [214] => [[File:Commercial laser lines.svg|thumb|upright=1.5|Wavelengths of commercially available lasers. Laser types with distinct laser lines are shown above the wavelength bar, while below are shown lasers that can emit in a wavelength range. The color codifies the type of laser material (see the figure description for more details).]] [215] => [216] => === Gas lasers === [217] => {{Main|Gas laser}} [218] => [219] => Following the invention of the HeNe gas laser, many other gas discharges have been found to amplify light coherently. [220] => Gas lasers using many different gases have been built and used for many purposes. The [[helium–neon laser]] (HeNe) can operate at many different wavelengths, however, the vast majority are engineered to lase at 633 nm; these relatively low-cost but highly coherent lasers are extremely common in optical research and educational laboratories. Commercial [[Carbon dioxide laser|carbon dioxide (CO2) 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 10.6 µm; such lasers are regularly used in industry for cutting and welding. The efficiency of a CO2 laser is unusually high: over 30%.{{cite web |url=http://www.phy.davidson.edu/stuhome/jimn/co2/pages/CO2Main.htm |last=Nolen |first=Jim |title=The Carbon Dioxide Laser |publisher=Davidson Physics |access-date=August 17, 2014 |author2=Derek Verno|archive-date=October 11, 2014 |archive-url=https://web.archive.org/web/20141011053320/http://www.phy.davidson.edu/stuhome/jimn/co2/pages/CO2Main.htm |url-status=live}} [[Ion laser|Argon-ion]] lasers can operate at several lasing transitions between 351 and 528.7 nm. Depending on the optical design one or more of these transitions can be lasing simultaneously; the most commonly used lines are 458 nm, 488 nm and 514.5 nm. A nitrogen [[TEA laser|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 337.1 nm.{{cite web [221] => | last = Csele [222] => | first = Mark [223] => | title = The TEA Nitrogen Gas Laser [224] => | work = Homebuilt Lasers Page [225] => |year=2004 [226] => | url = http://www.technology.niagarac.on.ca/people/mcsele/lasers/LasersTEA.htm [227] => | access-date =September 15, 2007 |archive-url = https://web.archive.org/web/20070911190723/http://www.technology.niagarac.on.ca/people/mcsele/lasers/LasersTEA.htm |archive-date = September 11, 2007}} Metal ion lasers are gas lasers that generate [[deep ultraviolet]] wavelengths. [[Helium]]-silver (HeAg) 224 nm and [[neon]]-copper (NeCu) 248 nm are two examples. Like all low-pressure gas lasers, the gain media of these lasers have quite narrow oscillation [[linewidth]]s, less than 3 [[GHz]] (0.5 [[picometers]]),{{cite web [228] => | title = Deep UV Lasers [229] => | publisher = Photon Systems, Covina, Calif [230] => | url = http://www.photonsystems.com/pdfs/duv-lasersource.pdf [231] => | archive-url = https://web.archive.org/web/20070701004933/http://www.photonsystems.com/pdfs/duv-lasersource.pdf [232] => | archive-date = July 1, 2007 [233] => | access-date =May 27, 2007 }} making them candidates for use in [[fluorescence]] suppressed [[Raman spectroscopy]]. [234] => [235] => [[Lasing without inversion|Lasing without maintaining the medium excited into a population inversion]] was demonstrated in 1992 in [[sodium]] gas and again in 1995 in [[rubidium]] gas by various international teams.{{cite journal |title=Lasing without inversion |year=2000 |last1=Mompart |first1=J. |last2=Corbalán |first2=R. |journal=J. Opt. B |volume=2 |issue=3 |doi=10.1088/1464-4266/2/3/201 |bibcode=2000JOptB...2R...7M |pages=R7–R24 |s2cid=121209763 }}{{cite book |last=Javan |first=A. |year=2000 |chapter=On knowing Marlan |title=Ode to a quantum physicist: A festschrift in honor of Marlan O. Scully |publisher=Elsevier}}{{Page missing|date=January 2024}} This was accomplished by using an external maser to induce "optical transparency" in the medium by introducing and destructively interfering the ground electron transitions between two paths so that the likelihood for the ground electrons to absorb any energy has been canceled. [236] => [237] => ==== Chemical lasers ==== [238] => [239] => [[Chemical laser]]s 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]] (2700–2900 nm) and the [[deuterium fluoride laser]] (3800 nm) the reaction is the combination of hydrogen or deuterium gas with combustion products of [[ethylene]] in [[nitrogen trifluoride]]. [240] => [241] => ==== Excimer lasers ==== [242] => [243] => [[Excimer laser]]s 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 that can only exist with one atom in an [[excited state|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 [[:Category:Noble gas compounds|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. Commonly used excimer molecules include ArF (emission at 193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm), and XeF (351 nm).{{cite book [244] => | first=D. | last=Schuocker | year=1998 [245] => | title=Handbook of the Eurolaser Academy [246] => | publisher=Springer | isbn=978-0-412-81910-0}}{{Page missing|date=January 2024}} [247] => The molecular [[fluorine]] laser, emitting at 157 nm in the vacuum ultraviolet is sometimes referred to as an excimer laser, however, this appears to be a misnomer since F2 is a stable compound. [248] => [249] => === Solid-state lasers === [250] => [251] => [[File:Starfield Optical Range - sodium laser.jpg|thumb|A 50 W [[frequency addition source of optical radiation|FASOR]], based on a Nd:YAG laser, used at the [[Starfire Optical Range]]]] [252] => [253] => [[Solid-state laser]]s use a crystalline or glass rod that 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 maintained in the dopant. These materials are pumped optically using a shorter wavelength than the lasing wavelength, often from a flash tube or 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. [254] => [255] => [[Neodymium]] is a common dopant in various solid-state laser crystals, including [[yttrium orthovanadate]] ([[Neodymium-doped yttrium orthovanadate|Nd:YVO4]]), [[yttrium lithium fluoride]] ([[Nd:YLF]]) and [[yttrium aluminium garnet]] ([[Nd:YAG]]). All these lasers can produce high powers in the [[infrared]] spectrum at 1064 nm. They are used for cutting, welding, and marking of metals and other materials, and also in [[spectroscopy]] and for pumping [[dye laser]]s. These lasers are also commonly [[second-harmonic generation|doubled]], [[third-harmonic generation|tripled]] or quadrupled in frequency to produce 532 nm (green, visible), 355 nm and 266 nm ([[ultraviolet|UV]]) beams, respectively. Frequency-doubled [[diode-pumped solid-state]] (DPSS) lasers are used to make bright green laser pointers. [256] => [257] => [[Ytterbium]], [[holmium]], [[thulium]], and [[erbium]] are other common "dopants" in solid-state lasers.{{Cite book |url=https://books.google.com/books?id=tygEGtu1b7MC&q=%C2%A0Ytterbium,+holmium,+thulium,+and+erbium+are+other+common+%22dopants%22+in+solid-state+lasers |title=Handbook of Optics, Third Edition Volume V: Atmospheric Optics, Modulators, Fiber Optics, X-Ray and Neutron Optics |last1=Bass |first1=Michael |last2=DeCusatis |first2=Casimer |last3=Enoch |first3=Jay |last4=Lakshminarayanan |first4=Vasudevan |last5=Li |first5=Guifang |last6=MacDonald |first6=Carolyn |last7=Mahajan |first7=Virendra |last8=Stryland |first8=Eric Van |date=2009-11-13 |publisher=McGraw Hill Professional |isbn=978-0-07-163314-7 |language=en |access-date=July 16, 2017 |archive-date=February 8, 2023 |archive-url=https://web.archive.org/web/20230208064634/https://books.google.com/books?id=tygEGtu1b7MC&q=%C2%A0Ytterbium,+holmium,+thulium,+and+erbium+are+other+common+%22dopants%22+in+solid-state+lasers |url-status=live}}{{Page missing|date=January 2024}} Ytterbium is used in crystals such as Yb:YAG, Yb:KGW, Yb:KYW, Yb:SYS, Yb:BOYS, Yb:CaF2, typically operating around 1020–1050 nm. 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 2097 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. [258] => [259] => [[Titanium]]-doped [[sapphire]] ([[Ti-sapphire laser|Ti:sapphire]]) produces a highly [[tunable laser|tunable]] [[infrared]] laser, commonly used for [[spectroscopy]]. It is also notable for use as a mode-locked laser producing [[ultrashort pulse]]s of extremely high peak power. [260] => [261] => Thermal limitations in solid-state lasers arise from unconverted pump power that heats the medium. This heat, when coupled with a high thermo-optic coefficient (d''n''/d''T'') can cause thermal lensing and reduce the quantum efficiency. Diode-pumped thin [[disk laser]]s 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.C. Stewen, M. Larionov, and A. Giesen, "Yb:YAG thin disk laser with 1 kW output power", in OSA Trends in Optics and Photonics, Advanced Solid-State Lasers, H. Injeyan, U. Keller, and C. Marshall, ed. (Optical Society of America, Washington, D.C., 2000) pp. 35–41. [262] => [263] => === Fiber lasers === [264] => {{Main|Fiber laser}} [265] => [266] => 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 laser]]s. Guiding of light allows extremely long gain regions providing good cooling conditions; fibers have a high surface area to volume ratio which allows efficient cooling. In addition, the fiber's waveguiding properties tend to reduce the thermal distortion of the beam. [[Erbium]] and [[ytterbium]] ions are common active species in such lasers. [267] => [268] => 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. [269] => [270] => Pump light can be used more efficiently by creating a [[fiber disk laser]], or a stack of such lasers. [271] => [272] => Fiber lasers, like other optical media, can suffer from the effects of [[photodarkening]] when they are exposed to radiation of certain wavelengths. In particular, this can lead to degradation of the material and loss in laser functionality over time. The exact causes and effects of this phenomenon vary from material to material, although it often involves the formation of [[Color center (crystallography)|color centers]].{{Cite web |last=Paschotta |first=Rüdiger |title=Photodarkening |url=https://www.rp-photonics.com/photodarkening.html |url-status=live |archive-url=https://web.archive.org/web/20230625023025/http://www.rp-photonics.com/photodarkening.html |archive-date=June 25, 2023 |access-date=2023-07-22 |website=www.rp-photonics.com |language=en}} [273] => [274] => === Photonic crystal lasers === [275] => [276] => [[Photonic crystal]] lasers are lasers based on nano-structures that provide the mode confinement and the [[Density of states|density of optical states]] (DOS) structure required for the feedback to take place.{{Clarify|date=February 2009}} They are typical micrometer-sized{{dubious|date=November 2010}} and tunable on the bands of the photonic crystals.{{cite journal |title=Ultraviolet photonic crystal laser |first=X. |last=Wu |volume=85 |issue=17 |date=October 25, 2004|journal=Applied Physics Letters |doi=10.1063/1.1808888|arxiv = physics/0406005 |bibcode = 2004ApPhL..85.3657W |page=3657 |s2cid=119460787 |display-authors=etal}}{{Clarify|date=February 2009}} [277] => [278] => === Semiconductor lasers === [279] => {{Main|Semiconductor lasers}} [280] => [281] => [[File:Diode laser.jpg|thumb|A 5.6 mm 'closed can' commercial laser diode, such as those used in a [[CD player|CD]] or [[DVD player]]]] [282] => [283] => Semiconductor lasers are [[diode]]s that are electrically pumped. Recombination of electrons and holes created by the applied current introduces optical gain. Reflection from the ends of the crystal forms an optical resonator, although the resonator can be external to the semiconductor in some designs. [284] => [285] => Commercial [[laser diode]]s emit at wavelengths from 375 nm to 3500 nm.{{cite web |url=http://www.hanel-photonics.com/laser_diode_market.html |title=Laser Diode Market |publisher=Hanel Photonics |access-date=Sep 26, 2014 |archive-date=December 7, 2015 |archive-url=https://web.archive.org/web/20151207211944/http://hanel-photonics.com/laser_diode_market.html |url-status=live }} Low to medium power laser diodes are used in [[laser pointer]]s, [[laser printer]]s and CD/DVD players. Laser diodes are also frequently used to optically [[laser pumping|pump]] other lasers with high efficiency. The highest-power industrial laser diodes, with power of up to 20 kW, are used in industry for cutting and welding.{{Cite web |url=https://www.industrial-lasers.com/articles/print/volume-29/issue-3/features/high-power-direct-diode-lasers-for-cutting-and-welding.html |title=High-power direct-diode lasers for cutting and welding |website=industrial-lasers.com |access-date=August 11, 2018 |archive-date=August 11, 2018|archive-url=https://web.archive.org/web/20180811195507/https://www.industrial-lasers.com/articles/print/volume-29/issue-3/features/high-power-direct-diode-lasers-for-cutting-and-welding.html |url-status=live}} External-cavity semiconductor lasers have a semiconductor active medium in a larger cavity. These devices can generate high power outputs with good beam quality, wavelength-tunable narrow-[[linewidth]] radiation, or ultrashort laser pulses. [286] => [287] => In 2012, [[Nichia]] and [[OSRAM]] developed and manufactured commercial high-power green laser diodes (515/520 nm), which compete with traditional diode-pumped solid-state lasers.{{cite web |url=http://www.nichia.co.jp/en/product/laser.html |title=LASER Diode |work=nichia.co.jp|access-date=March 18, 2014 |archive-date=March 18, 2014 |archive-url=https://web.archive.org/web/20140318093016/http://www.nichia.co.jp/en/product/laser.html |url-status=live}}{{cite web |url=http://www.osram-os.com/osram_os/en/products/product-catalog/laser-diodes/visible-laser/green-laser/index.jsp |title=Green Laser |date=August 19, 2015 |work=osram-os.com |access-date=March 18, 2014 |archive-date=March 18, 2014 |archive-url=https://web.archive.org/web/20140318104254/http://www.osram-os.com/osram_os/en/products/product-catalog/laser-diodes/visible-laser/green-laser/index.jsp |url-status=live}} [288] => [289] => Vertical cavity surface-emitting lasers ([[VCSEL]]s) 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. As of 2005, only 850 nm VCSELs are widely available, with 1300 nm VCSELs beginning to be commercialized,{{cite web |url=http://lfw.pennnet.com/Articles/Article_Display.cfm?ARTICLE_ID=243400&p=12 |title=Picolight ships first 4-Gbit/s 1310-nm VCSEL transceivers |work=Laser Focus World Online |date=December 9, 2005 |access-date=May 27, 2006 |archive-url=https://web.archive.org/web/20060313161940/http://lfw.pennnet.com/Articles/Article_Display.cfm?ARTICLE_ID=243400&p=12 |archive-date=March 13, 2006}} and 1550 nm devices an area of research. [[VECSEL]]s are external-cavity VCSELs. [[Quantum cascade laser]]s are semiconductor lasers that have an active transition between energy ''sub-bands'' of an electron in a structure containing several [[quantum well]]s. [290] => [291] => 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 interconnect]]s) 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 that 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.{{cite journal|title=Monolithically Integrated High-β Nanowire Lasers on Silicon |first1=B. |last1=Mayer |first2=L. |last2=Janker |first3=B. |last3=Loitsch |first4=J. |last4=Treu |first5=T. |last5=Kostenbader |first6=S. |last6=Lichtmannecker |first7=T. |last7=Reichert |first8=S. |last8=Morkötter |first9=M. |last9=Kaniber |first10=G. |last10=Abstreiter |first11=C. |last11=Gies |first12=G. |last12=Koblmüller |first13=J.J. |last13=Finley |date=January 13, 2016 |journal=Nano Letters |volume=16 |issue=1 |pages=152–156 |doi=10.1021/acs.nanolett.5b03404 |pmid=26618638 |bibcode=2016NanoL..16..152M}} These heterostructure nanowire lasers capable of optical interconnects in silicon are also capable of emitting pairs of phase-locked picosecond pulses with a repetition frequency up to 200 GHz, allowing for on-chip optical signal processing. Another type is a [[Raman laser]], which takes advantage of [[Raman scattering]] to produce a laser from materials such as silicon. [292] => [293] => === Dye lasers === [294] => [[File:Coherent 899 dye laser.jpg|thumb|Close-up of a table-top dye laser based on [[Rhodamine 6G]]]] [295] => [296] => [[Dye laser]]s 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 [[femtosecond]]s). Although these [[tunable laser]]s 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. [297] => [298] => [[Bubble laser]]s are dye lasers that use a [[Bubble (physics)|bubble]] as the optical resonator. [[Whispering gallery mode]]s in the bubble produce an output spectrum composed of hundreds of evenly spaced peaks; a [[frequency comb]]. The spacing of the whispering gallery modes is directly related to the bubble circumference, allowing bubble lasers to be used as highly sensitive pressure sensors.{{cite web |last1=Miller |first1=Johanna |title=Bubble lasers can be sturdy and sensitive |url=https://pubs.aip.org/physicstoday/article/77/3/12/3267372/Bubble-lasers-can-be-sturdy-and-sensitiveMade-of |website=Physics Today |publisher=American Institute of Physics |access-date=2 April 2024}} [299] => [300] => === Free-electron lasers === [301] => [[File:FELIX.jpg|thumb|The free-electron laser ''FELIX'' at the FOM Institute for Plasma Physics Rijnhuizen, [[Nieuwegein]]]] [302] => [303] => [[Free-electron laser]]s (FEL) 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''. [304] => [305] => === Exotic media === [306] => [307] => The pursuit of a high-quantum-energy laser using transitions between [[Nuclear isomer|isomeric states]] of an [[atomic nucleus]] has been the subject of wide-ranging academic research since the early 1970s. Much of this is summarized in three review articles.{{cite journal |last1=Baldwin |first1=G.C. |last2=Solem |first2=J.C. |last3=Gol'danskii |first3=V. I.|year=1981 |title=Approaches to the development of gamma-ray lasers |journal=Reviews of Modern Physics |volume=53 |issue=4 |pages=687–744 |bibcode = 1981RvMP...53..687B |doi = 10.1103/RevModPhys.53.687}}{{cite journal |last1=Baldwin |first1=G.C. |last2=Solem |first2=J.C. |year=1995 |title=Recent proposals for gamma-ray lasers |journal=Laser Physics |volume=5 |issue=2 |pages=231–239}}{{cite journal |last1=Baldwin |first1=G.C. |last2=Solem |first2=J.C. |year=1997 |title=Recoilless gamma-ray lasers |journal=Reviews of Modern Physics |volume=69 |issue=4 |pages=1085–1117 |bibcode=1997RvMP...69.1085B|doi=10.1103/RevModPhys.69.1085 |url=https://zenodo.org/record/1233965 |access-date=June 13, 2019 |archive-date=July 28, 2019 |archive-url=https://web.archive.org/web/20190728114208/https://zenodo.org/record/1233965 |url-status=live}} This research has been international in scope but mainly based in the former Soviet Union and the United States. While many scientists remain optimistic that a breakthrough is near, an operational [[gamma-ray laser]] is yet to be realized.{{cite journal |last1=Baldwin |first1=G.C. |last2=Solem |first2=J.C. |year=1982 |title=Is the time ripe? Or must we wait so long for breakthroughs?|journal=Laser Focus |volume=18 |issue=6 |pages=6&8}} [308] => [309] => {{Anchor|multiphoton2016-01-30}}Some of the early studies were directed toward short pulses of neutrons exciting the upper isomer state in a solid so the gamma-ray transition could benefit from the line-narrowing of [[Mössbauer effect]].{{cite journal |last=Solem |first=J.C. |year=1979 |title=On the feasibility of an impulsively driven gamma-ray laser |journal=Los Alamos Scientific Laboratory Report LA-7898 |doi=10.2172/6010532 |osti=6010532}}{{Page missing|date=January 2024}}{{cite journal |last1=Baldwin |first1=G.C. |last2=Solem |first2=J.C.|year=1979 |title=Maximum density and capture rates of neutrons moderated from a pulsed source |journal=Nuclear Science & Engineering |volume=72 |issue=3 |pages=281–289 |url=http://www.ans.org/pubs/journals/nse/a_20384|doi=10.13182/NSE79-A20384 |bibcode=1979NSE....72..281B |access-date=January 13, 2016 |archive-date=February 7, 2016 |archive-url=https://web.archive.org/web/20160207090745/http://www.ans.org/pubs/journals/nse/a_20384 |url-status=live}} In conjunction, several advantages were expected from two-stage pumping of a three-level system.{{cite journal |last1=Baldwin |first1=G.C. |last2=Solem |first2=J.C. |year=1980|title=Two-stage pumping of three-level Mössbauer gamma-ray lasers |journal=Journal of Applied Physics |volume=51 |issue=5 |pages=2372–2380 |bibcode = 1980JAP....51.2372B |doi = 10.1063/1.328007}} It was conjectured that the nucleus of an atom, embedded in the near field of a laser-driven coherently-oscillating electron cloud would experience a larger dipole field than that of the driving laser.{{cite conference |last=Solem |first=J.C. |title=AIP Conference Proceedings |year=1986 |chapter=Interlevel transfer mechanisms and their application to grasers |conference=Proceedings of Advances in Laser Science-I, First International Laser Science Conference, Dallas, TX 1985 (American Institute of Physics, Optical Science and Engineering, Series 6) |volume=146 |pages=22–25 |doi=10.1063/1.35861 |bibcode=1986AIPC..146...22S |chapter-url=https://digital.library.unt.edu/ark:/67531/metadc1105924/ |access-date=November 27, 2018 |archive-date=November 27, 2018 |archive-url=https://web.archive.org/web/20181127110611/https://digital.library.unt.edu/ark:/67531/metadc1105924/ |url-status=live}}{{cite conference |last1=Biedenharn |first1=L.C. |last2=Boyer |first2=K. |last3=Solem |first3=J.C. |title=AIP Conference Proceedings |year=1986 |chapter=Possibility of grasing by laser-driven nuclear excitation |conference=Proceedings of AIP Advances in Laser Science-I, Dallas, TX, November 18–22, 1985 |volume=146 |pages=50–51|doi=10.1063/1.35928|bibcode=1986AIPC..146...50B}} Furthermore, the nonlinearity of the oscillating cloud would produce both spatial and temporal harmonics, so nuclear transitions of higher multipolarity could also be driven at multiples of the laser frequency.{{cite conference |last1=Rinker |first1=G.A. |last2=Solem |first2=J.C. |last3=Biedenharn |first3=L.C. |editor1-first=Randy C |editor1-last=Jones |title=Calculation of harmonic radiation and nuclear coupling arising from atoms in strong laser fields |book-title=Proc. SPIE 0875, Short and Ultrashort Wavelength Lasers |conference=1988 Los Angeles Symposium: O-E/LASE '88, 1988, Los Angeles, CA, United States |date=April 27, 1988 |publisher=International Society for Optics and Photonics |volume=146 |pages=92–101 |doi=10.1117/12.943887 |series=Short and Ultrashort Wavelength Lasers}}{{cite journal |last1=Rinker |first1=G. A. |last2=Solem |first2=J.C. |last3=Biedenharn |first3=L.C. |year=1987 |title=Nuclear interlevel transfer driven by collective outer shell electron excitations |journal=Proceedings of the Second International Laser Science Conference, Seattle, WA (Advances in Laser Science-II) |editor=Lapp, M. |editor2=Stwalley, W.C. |editor3=Kenney-Wallace G.A. |publisher=American Institute of Physics |location=New York |volume=160 |pages=75–86 |oclc=16971600}}{{cite journal |last=Solem |first=J.C. |year=1988 |title=Theorem relating spatial and temporal harmonics for nuclear interlevel transfer driven by collective electronic oscillation |journal=Journal of Quantitative Spectroscopy and Radiative Transfer |volume=40 |issue=6 |pages=713–715 |url=https://zenodo.org/record/1253954 |bibcode=1988JQSRT..40..713S |doi=10.1016/0022-4073(88)90067-2 |access-date=September 8, 2019 |archive-date=March 18, 2020 |archive-url=https://web.archive.org/web/20200318062519/https://zenodo.org/record/1253954 |url-status=live}}{{cite journal |last1=Solem |first1=J.C. |last2=Biedenharn |first2=L.C. |year=1987 |title=Primer on coupling collective electronic oscillations to nuclei |journal=Los Alamos National Laboratory Report LA-10878 |url=http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/19/009/19009581.pdf |bibcode=1987pcce.rept.....S |page=1 |access-date=January 13, 2016 |archive-date=March 4, 2016 |archive-url=https://web.archive.org/web/20160304060942/http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/19/009/19009581.pdf |url-status=live}}{{cite journal |last1=Solem |first1=J.C. |last2=Biedenharn |first2=L.C.|year=1988|title=Laser coupling to nuclei via collective electronic oscillations: A simple heuristic model study |journal=Journal of Quantitative Spectroscopy and Radiative Transfer |volume=40 |issue=6 |pages=707–712 |bibcode = 1988JQSRT..40..707S |doi = 10.1016/0022-4073(88)90066-0 }}{{cite conference |last1=Boyer |first1=K. |last2=Java |first2=H. |last3=Luk |first3=T.S.|last4=McIntyre |first4=I.A.|last5=McPherson |first5=A.|last6=Rosman |first6=R.|last7=Solem |first7=J.C.|last8=Rhodes |first8=C.K. |last9=Szöke |first9=A. |year=1987 |title=Discussion of the role of many-electron motions in multiphoton ionization and excitation |book-title=Proceedings of International Conference on Multiphoton Processes (ICOMP) IV, July 13–17, 1987, Boulder, CA |editor=Smith, S. |editor2=Knight, P. |publisher=Cambridge University Press |location=Cambridge, England |pages=58 |osti=10147730}}{{cite journal |last1=Biedenharn |first1=L.C. |last2=Rinker |first2=G.A. |last3=Solem |first3=J.C. |year=1989 |title=A solvable approximate model for the response of atoms subjected to strong oscillatory electric fields |journal=Journal of the Optical Society of America B|volume=6 |issue=2 |pages=221–227 |bibcode=1989JOSAB...6..221B|doi=10.1364/JOSAB.6.000221 |url=https://zenodo.org/record/1235650 |access-date=June 13, 2019 |archive-date=March 21, 2020 |archive-url=https://web.archive.org/web/20200321181221/https://zenodo.org/record/1235650 |url-status=live}} [310] => [311] => In September 2007, the [[BBC News]] reported that there was speculation about the possibility of using [[positronium]] [[annihilation]] to drive a very powerful [[gamma ray]] laser.{{cite news |url=http://news.bbc.co.uk/2/hi/science/nature/6991030.stm |title=Mirror particles form new matter |first=Jonathan |last=Fildes |date=September 12, 2007 |work=BBC News |access-date=May 22, 2008 |archive-date=April 21, 2009 |archive-url=https://web.archive.org/web/20090421143709/http://news.bbc.co.uk/2/hi/science/nature/6991030.stm |url-status=live}} 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. [312] => [313] => Space-based [[X-ray laser]]s pumped by a nuclear explosion have also been proposed as antimissile weapons.{{cite journal |first=Jeff |last=Hecht |title=The history of the x-ray laser |journal=Optics and Photonics News |volume=19 |issue=5 |date=May 2008 |pages=26–33 |doi=10.1364/opn.19.5.000026|bibcode = 2008OptPN..19R..26H}}{{cite magazine |first=Clarence A. |last=Robinson |title=Advance made on high-energy laser |magazine=Aviation Week & Space Technology |date=February 23, 1981 |pages=25–27}} Such devices would be one-shot weapons. [314] => [315] => Living cells have been used to produce laser light.{{cite news |url=https://www.bbc.co.uk/news/science-environment-13725719 |title=Laser is produced by a living cell |first=Jason |last=Palmer |date=June 13, 2011 |newspaper=BBC News |access-date=June 13, 2011 |archive-date=June 13, 2011 |archive-url=https://web.archive.org/web/20110613112054/http://www.bbc.co.uk/news/science-environment-13725719 |url-status=live}}{{cite journal |title=Single-cell biological lasers |author1=Malte C. Gather |author2=Seok Hyun Yun |name-list-style=amp |date=June 12, 2011 |journal=Nature Photonics |doi=10.1038/nphoton.2011.99 |volume=5 |issue=7 |pages=406–410|bibcode=2011NaPho...5..406G}} The cells were genetically engineered to produce [[green fluorescent protein]], which served as the laser's gain medium. 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 intensely directed green laser light. [316] => [317] => === Natural lasers === [318] => [319] => Like [[astrophysical maser]]s, irradiated planetary or stellar gases may amplify light producing a natural laser.{{cite news |last1=Chen |first1=Sophia |title=Alien Light |url=https://spie.org/news/photonics-focus/janfeb-2020/astrophysical-lasers?SSO=1 |access-date=9 February 2021 |work=[[SPIE]] |date=1 January 2020 |archive-date=April 14, 2021 |archive-url=https://web.archive.org/web/20210414143405/https://spie.org/news/photonics-focus/janfeb-2020/astrophysical-lasers?SSO=1 |url-status=live}} [[Mars]],{{cite journal |last1=Mumma |first1=Michael J |title=Discovery of Natural Gain Amplification in the 10-Micrometer Carbon Dioxide Laser Bands on Mars: A Natural Laser |journal=[[Science (journal)|Science]] |date=3 April 1981 |volume=212 |issue=4490 |pages=45–49 |doi=10.1126/science.212.4490.45 |pmid=17747630 |bibcode=1981Sci...212...45M |url=https://www.science.org/doi/10.1126/science.212.4490.45 |access-date=February 9, 2021 |archive-date=February 17, 2022 |archive-url=https://web.archive.org/web/20220217063028/https://www.science.org/doi/10.1126/science.212.4490.45 |url-status=live}} [[Venus]] and [[MWC 349]] exhibit this phenomenon. [320] => [321] => == Uses == [322] => {{Main|List of applications for lasers}} [323] => [[File:Laser sizes.jpg|thumb|Lasers range in size from microscopic [[diode laser]]s (''top'') with numerous applications, to football field sized [[neodymium]] glass lasers (bottom) used for [[inertial confinement fusion]], [[nuclear weapon]]s research and other high energy density physics experiments]] [324] => [325] => When lasers were invented in 1960, they were called "a solution looking for a problem".{{cite book |title=A Century of Nature: Twenty-One Discoveries that Changed Science and the World |author=Charles H. Townes |author-link=Charles Hard Townes |chapter=The first laser |chapter-url=http://www.press.uchicago.edu/Misc/Chicago/284158_townes.html |editor1=Laura Garwin |editor1-link= Laura Garwin |editor2=Tim Lincoln |publisher=University of Chicago Press |year=2003 |pages=[https://archive.org/details/centuryofnaturet00garw/page/107 107–12] |isbn=978-0-226-28413-2 |url-access=registration |url=https://archive.org/details/centuryofnaturet00garw/page/107}} Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including [[consumer electronics]], information technology, science, medicine, industry, [[law enforcement]], entertainment, and the [[Laser applications#Military|military]]. [[Fiber-optic communication]] using lasers is a key technology in modern communications, allowing services such as the [[Internet]]. [326] => [327] => The first widely noticeable use of lasers was 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 laser-equipped device to become common, beginning in 1982 followed shortly by [[laser printer]]s. [328] => [329] => Some other uses are: [330] => * Communications: besides [[fiber-optic communication]], lasers are used for [[free-space optical communication]], including [[laser communication in space]] [331] => * Medicine: see [[#In medicine|below]] [332] => * Industry: [[Laser cutting|cutting]] including [[Laser converting|converting]] thin materials, [[laser welding|welding]], material [[heat treatment]], [[laser marking|marking parts]] ([[Laser engraving|engraving]] and [[Laser bonding|bonding]]), [[additive manufacturing]] or [[3D printing]] processes such as [[selective laser sintering]] and [[selective laser melting]], [[laser metal deposition]], and non-contact measurement of parts and [[3D scanning]], and [[laser cleaning]]. [333] => * Military: marking targets, guiding [[munition]]s, [[Airborne Laser|missile defense]], [[DIRCM|electro-optical countermeasures (EOCM)]], [[lidar]], blinding troops, [[Laser sight (firearms)|firearms sight]]. See [[#As weapons|below]] [334] => * [[Law enforcement agency|Law enforcement]]: [[LIDAR traffic enforcement]]. Lasers are used for latent [[fingerprint]] detection in the [[forensic identification]] fieldDalrymple B.E., Duff J.M., Menzel E.R. "Inherent fingerprint luminescence – detection by laser". ''Journal of Forensic Sciences'', 22(1), 1977, 106–115Dalrymple B.E. "Visible and infrared luminescence in documents : excitation by laser". ''Journal of Forensic Sciences'', 28(3), 1983, 692–696 [335] => * Research: [[spectroscopy]], [[laser ablation]], laser [[annealing (metallurgy)|annealing]], laser [[scattering]], laser [[interferometry]], [[lidar]], [[laser capture microdissection]], [[fluorescence microscopy]], [[metrology]], [[laser cooling]] [336] => * Commercial products: [[laser printer]]s, [[barcode scanner]]s, [[thermometer]]s, [[laser pointer]]s, [[holograms]], [[bubblegram]]s [337] => * Entertainment: [[optical discs]], [[laser lighting display]]s, [[laser turntable]]s. [338] => * Informational markings: Laser lighting display technology can be used to project informational markings onto surfaces such as playing fields, roads, runways, or warehouse floors.{{cite web |title=Laser Technology Enhances Experience for Sports Fans, Refs |url=https://www.photonics.com/Article.aspx?PID=5&VID=116&IID=774&Tag=Features&AID=56631 |website=Photonics.com |date=September 10, 2014 |access-date=August 23, 2023}}{{cite web |title=Front Lines |first=Susan |last=Woods |work=Shop Floor Lasers |url=https://fsmdirect.com/front-lines/ |date= April 13, 2015 |access-date=August 23, 2023}}{{cite web |title=Football Tech That's More Than a Laser and Light Show [339] => |first=Kevin |last=Randall |work=[[The New York Times]] |url= https://www.nytimes.com/2022/04/20/sports/football/usfl-technology-ball-spotting.html?smid [340] => |date= April 20, 2022 |access-date=August 30, 2023}} [341] => [342] => In 2004, excluding diode lasers, approximately 131,000 lasers were sold with a value of {{US$|2.19|link=yess}} billion.{{cite magazine |last1=Kincade |first1=Kathy |first2=Stephen |last2=Anderson |date=January 1, 2005 |title=Laser Marketplace 2005: Consumer applications boost laser sales 10% |magazine=Laser Focus World |volume=41 |issue=1 |url=http://www.laserfocusworld.com/articles/print/volume-41/issue-1/features/laser-marketplace-2005/consumer-applications-boost-laser-sales-10.html |access-date=April 6, 2015 |archive-date=April 13, 2015 |archive-url=https://web.archive.org/web/20150413001047/http://www.laserfocusworld.com/articles/print/volume-41/issue-1/features/laser-marketplace-2005/consumer-applications-boost-laser-sales-10.html |url-status=live}} In the same year, approximately 733 million diode lasers, valued at {{US$|3.20}} billion, were sold.{{cite magazine |last1=Steele |first1=Robert V. |date=February 1, 2005 |title=Diode-laser market grows at a slower rate |magazine=Laser Focus World |volume=41 |issue=2 |url=http://www.laserfocusworld.com/articles/print/volume-41/issue-2/features/diode-laser-market-grows-at-a-slower-rate.html |access-date=April 6, 2015 |archive-date=April 12, 2015 |archive-url=https://web.archive.org/web/20150412234959/http://www.laserfocusworld.com/articles/print/volume-41/issue-2/features/diode-laser-market-grows-at-a-slower-rate.html |url-status=live}} [343] => [344] => === In medicine === [345] => {{Main|Laser medicine|Lasers in cancer treatment}} [346] => [347] => Lasers have many uses in medicine, including [[laser surgery]] (particularly [[Laser eye surgery|eye surgery]]), laser healing (photobiomodulation therapy), [[kidney stone]] treatment, [[Scanning laser ophthalmoscopy|ophthalmoscopy]], and cosmetic skin treatments such as [[acne]] treatment, [[cellulite]] and [[striae]] reduction, and [[Laser hair removal|hair removal]]. [348] => [349] => Lasers are used to treat [[cancer]] by shrinking or destroying [[Neoplasm|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 cancer|cervical]], [[penile cancer|penile]], [[vaginal cancer|vaginal]], [[vulvar cancer|vulvar]], and [[non-small cell lung cancer]]. Laser therapy is often combined with other treatments, such as [[surgery]], [[chemotherapy]], or [[radiation therapy]]. [[Laser ablation|Laser-induced interstitial thermotherapy]] (LITT), or interstitial laser [[Laser coagulation|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.{{Cite web |url=https://medlineplus.gov/ency/patientinstructions/000905.htm|title=Laser therapy for cancer: MedlinePlus Medical Encyclopedia|website=medlineplus.gov|language=en |access-date= December 15, 2017 |archive-date=February 24, 2021 |archive-url=https://web.archive.org/web/20210224172003/https://medlineplus.gov/ency/patientinstructions/000905.htm |url-status=live}}{{citation-attribution |1={{cite web |url=https://www.cancer.gov/about-cancer/treatment/types/surgery/lasers-fact-sheet |title=Lasers in Cancer Treatment |date= September 13, 2011 |publisher=National Institutes of Health, National Cancer Institute |access-date= December 15, 2017|archive-date=April 5, 2020|archive-url=https://web.archive.org/web/20200405184554/https://www.cancer.gov/about-cancer/treatment/types/surgery/lasers-fact-sheet |url-status=live}}}} [350] => [351] => === As weapons === [352] => {{Main|Laser weapon}} [353] => {{summarize|from|Laser weapon|date=December 2019}} [354] => [355] => A '''laser weapon''' is a laser that is used as a [[directed-energy weapon]]. [356] => [357] => [[File:THEL-ACTD.jpg|thumb|The US–Israeli [[Tactical High Energy Laser|Tactical High Energy weapon]] has been used to shoot down rockets and artillery shells]] [358] => [359] => === Hobbies === [360] => [361] => In recent years, some hobbyists have taken an interest in lasers. Lasers used by hobbyists are generally of class IIIa or IIIb {{xref|(see {{slink||Safety}})}}, although some have made their own class IV types.[http://www.powerlabs.org/laser.htm PowerLabs CO2 LASER!] {{Webarchive |url=https://web.archive.org/web/20050814004546/http://www.powerlabs.org/laser.htm |date=August 14, 2005 }} Sam Barros June 21, 2006. Retrieved January 1, 2007. However, compared to other hobbyists, laser hobbyists are far less common, due to the cost and potential dangers involved. 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 burner]]s.{{cite web |first=Stephanie |last=Maks |url=http://planetstephanie.net/dvd-laser/ |title=Howto: Make a DVD burner into a high-powered laser |work=Transmissions from Planet Stephanie |access-date=April 6, 2015 |archive-date=February 17, 2022 |archive-url=https://web.archive.org/web/20220217050834/http://planetstephanie.net/dvd-laser/ |url-status=dead}} [362] => [363] => 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. [364] => [365] => === Examples by power === [366] => [[File:Lying down on the VLT platform.jpg|thumb|Laser application in astronomical [[adaptive optics]] imaging]] [367] => [368] => 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. [369] => [370] => {| class="wikitable mw-collapsible" [371] => |+ The continuous or average power required for some uses: [372] => |- [373] => ! Power !! Use [374] => |- [375] => |align=right| {{nowrap|1–5 mW}} || [[Laser pointer]]s [376] => |- [377] => |align=right| {{nowrap|5 mW}} || [[CD-ROM]] drive [378] => |- [379] => |align=right| {{nowrap|5–10 mW}} || [[DVD player]] or [[DVD-ROM drive]] [380] => |- [381] => |align=right| {{nowrap|100 mW}} || High-speed [[CD-RW]] burner [382] => |- [383] => |align=right| {{nowrap|250 mW}} || Consumer 16× [[DVD-R]] burner [384] => |- [385] => |align=right| {{nowrap|400 mW}} || DVD 24× dual-layer recording{{cite web |url=http://elabz.com/laser-diode-power-output-based-on-dvd-rrw-specs/ |title=Laser Diode Power Output Based on DVD-R/RW specs |date=April 10, 2011 |publisher=elabz.com |access-date=December 10, 2011 |archive-date=November 22, 2011 |archive-url=https://web.archive.org/web/20111122224656/http://elabz.com/laser-diode-power-output-based-on-dvd-rrw-specs/ |url-status=live}} [386] => |- [387] => |align=right| {{nowrap|1 W}} || Green laser in [[Holographic Versatile Disc]] prototype development [388] => |- [389] => |align=right| {{nowrap|1–20 W}} || Output of the majority of commercially available solid-state lasers used for [[Micromachinery|micro machining]] [390] => |- [391] => |align=right| {{nowrap|30–100 W}} || Typical sealed CO2 surgical lasers{{cite web |url=https://aesculight.com/case-studies/what-do-independent-laser-surgery-experts-advise-on-how-to-select-a-surgical-veterinary-laser/ |title=How to select a surgical veterinary laser |last=Peavy |first=George M. |work=Aesculight |access-date=March 30, 2016 |date=January 23, 2014 |archive-date=April 19, 2016 |archive-url=https://web.archive.org/web/20160419134604/https://aesculight.com/case-studies/what-do-independent-laser-surgery-experts-advise-on-how-to-select-a-surgical-veterinary-laser/ |url-status=live}} [392] => |- [393] => |align=right| {{nowrap|100–3000 W}} || Typical sealed CO2 lasers used in industrial [[laser cutting]] [394] => |} [395] => [396] => Examples of pulsed systems with high peak power: [397] => * 700 [[terawatt|TW]] (700×1012 W){{mdash}}[[National Ignition Facility]], a 192-beam, 1.8-megajoule laser system adjoining a 10-meter-diameter target chamberHeller, Arnie, "[http://www.llnl.gov/str/JulAug05/VanArsdall.html Orchestrating the world's most powerful laser] {{Webarchive |url=https://web.archive.org/web/20081121173542/https://www.llnl.gov/str/JulAug05/VanArsdall.html |date=November 21, 2008}}." ''Science and Technology Review''. Lawrence Livermore National Laboratory, July/August 2005. Retrieved May 27, 2006. [398] => * 10 [[petawatt|PW]] (10×1015 W){{mdash}}world's most powerful laser as of 2019, located at the [[Extreme Light Infrastructure|ELI-NP]] facility in [[Măgurele]], Romania.{{cite web |last1=Dragan |first1=Aurel |title=Magurele Laser officially becomes the most powerful laser in the world |url=https://business-review.eu/tech/magurele-laser-part-of-eli-project-reached-maximum-power-of-10-petawats-197989 |website=Business Review |access-date=23 March 2021 |date=13 March 2019 |archive-date=April 14, 2021 |archive-url=https://web.archive.org/web/20210414114412/https://business-review.eu/tech/magurele-laser-part-of-eli-project-reached-maximum-power-of-10-petawats-197989 |url-status=live}} [399] => [400] => == Safety == [401] => {{Main|Laser safety}} [402] => [403] => {{multiple image |width=155 |image1=DIN 4844-2 Warnung vor Laserstrahl D-W010.svg |alt1=European laser warning symbol |image2=Laser label 2.jpg |alt2=US laser warning label |footer=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}} [404] => [405] => Even the first laser was recognized as being potentially dangerous. [[Theodore Maiman]] characterized the first laser as having the power of one "Gillette" as it could burn through one [[Global Gillette|Gillette]] [[razor]] blade.{{cite magazine |last=Zurer | first=Rachel | title=Three Smart Things About Lasers | magazine=WIRED | date=December 27, 2011 | url=https://www.wired.com/2011/12/st-3st-lasers/ | access-date=February 16, 2024}}{{cite web | last=Jr | first=John Johnson | title=Theodore Maiman, 79; harnessed light to build the world's first working laser | website=Los Angeles Times | date=May 11, 2007 | url=https://www.latimes.com/archives/la-xpm-2007-may-11-me-maiman11-story.html | access-date=February 16, 2024}} 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 [[human eye|eye]] into an extremely small spot on the [[retina]], resulting in localized burning and permanent damage in seconds or even less time. [406] => [407] => Lasers are usually labeled with a safety class number, which identifies how dangerous the laser is: [408] => * Class 1 is inherently safe, usually because the light is contained in an enclosure, for example in CD players [409] => * Class 2 is safe during normal use; the [[blink reflex]] of the eye will prevent damage. Usually up to 1 mW power, for example, laser pointers. [410] => * Class 3R (formerly IIIa) lasers are usually up to 5 mW and involve a small risk of eye damage within the time of the blink reflex. Staring into such a beam for several seconds is likely to cause damage to a spot on the retina. [411] => * Class 3B lasers (5–499 mW) can cause immediate eye damage upon exposure. [412] => * Class 4 lasers (≥ 500 mW) can burn skin, and in some cases, even scattered light from these lasers can cause eye and/or skin damage. Many industrial and scientific lasers are in this class. [413] => 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. [414] => [415] => Infrared lasers with wavelengths longer than about 1.4{{nbsp}}micrometers are often referred to as "eye-safe", because the cornea tends to absorb light at these wavelengths, protecting the retina from damage. 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. [416] => [417] => 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. [418] => [419] => Cameras based on [[charge-coupled device]]s may be more sensitive to laser damage than biological eyes.{{cite news |last1=Hecht |first1=Jeff |title=Can Lidars Zap Camera Chips? |url=https://spectrum.ieee.org/cars-that-think/transportation/sensors/keeping-lidars-from-zapping-camera-chips |access-date=1 February 2019 |work=[[IEEE Spectrum]] |date= January 24, 2018 |archive-date=February 2, 2019 |archive-url=https://web.archive.org/web/20190202041923/https://spectrum.ieee.org/cars-that-think/transportation/sensors/keeping-lidars-from-zapping-camera-chips |url-status=live}} [420] => [421] => == See also == [422] => [423] => {{div col|colwidth=18em}} [424] => * [[Coherent perfect absorber]] [425] => * [[Homogeneous broadening]] [426] => * [[Laser linewidth]] [427] => * [[List of laser articles]] [428] => * [[List of light sources]] [429] => * [[Nanolaser]] [430] => * [[Sound amplification by stimulated emission of radiation]] [431] => * [[Spaser]] [432] => * [[Fabry–Pérot interferometer]] [433] => {{div col end}} [434] => [435] => == References == [436] => {{reflist}} [437] => [438] => == Further reading == [439] => === Books === [440] => * Bertolotti, Mario (1999, trans. 2004). ''The History of the Laser''. Institute of Physics. {{ISBN|0-7503-0911-3}}. [441] => * Bromberg, Joan Lisa (1991). ''The Laser in America, 1950–1970''. MIT Press. {{ISBN|978-0-262-02318-4}}. [442] => * Csele, Mark (2004). ''Fundamentals of Light Sources and Lasers''. Wiley. {{ISBN|0-471-47660-9}}. [443] => * Koechner, Walter (1992). ''Solid-State Laser Engineering''. 3rd ed. Springer-Verlag. {{ISBN|0-387-53756-2}}. [444] => * Siegman, Anthony E. (1986). ''Lasers''. University Science Books. {{ISBN|0-935702-11-3}}. [445] => * [[William T. Silfvast|Silfvast, William T.]] (1996). ''Laser Fundamentals''. Cambridge University Press. {{ISBN|0-521-55617-1}}. [446] => * Svelto, Orazio (1998). ''Principles of Lasers''. 4th ed. Trans. David Hanna. Springer. {{ISBN|0-306-45748-2}}. [447] => * {{cite book |last=Taylor |first=Nick |title=LASER: The inventor, the Nobel laureate, and the thirty-year patent war |year=2000 |publisher=Simon & Schuster |location=New York |isbn=978-0-684-83515-0 }} [448] => * Wilson, J. & Hawkes, J.F.B. (1987). ''Lasers: Principles and Applications''. Prentice Hall International Series in Optoelectronics, [[Prentice Hall]]. {{ISBN|0-13-523697-5}}. [449] => * Yariv, Amnon (1989). ''Quantum Electronics''. 3rd ed. Wiley. {{ISBN|0-471-60997-8}}. [450] => [451] => === Periodicals === [452] => * ''[[Applied Physics B: Lasers and Optics]]'' ({{ISSN|0946-2171}}) [453] => * ''[[IEEE Journal of Lightwave Technology]]'' ({{ISSN|0733-8724}}) [454] => * ''[[IEEE Journal of Quantum Electronics]]'' ({{ISSN|0018-9197}}) [455] => * ''[[IEEE Journal of Selected Topics in Quantum Electronics]]'' ({{ISSN|1077-260X}}) [456] => * ''[[IEEE Photonics Technology Letters]]'' ({{ISSN|1041-1135}}) [457] => * ''[[Journal of the Optical Society of America B: Optical Physics]]'' ({{ISSN|0740-3224}}) [458] => * ''[[Laser Focus World]]'' ({{ISSN|0740-2511}}) [459] => * ''[[Optics Letters]]'' ({{ISSN|0146-9592}}) [460] => * ''[[Photonics Spectra]]'' ({{ISSN|0731-1230}}) [461] => [462] => == External links == [463] => [464] => {{Commons category|Lasers}} [465] => [466] => * [http://www.rp-photonics.com/encyclopedia.html Encyclopedia of laser physics and technology by Rüdiger Paschotta] [467] => * [http://www.repairfaq.org/sam/lasersam.htm A Practical Guide to Lasers for Experimenters and Hobbyists by Samuel M. Goldwasser] [468] => * [http://www.technology.niagarac.on.ca/staff/mcsele/lasers/index.html Homebuilt Lasers Page by Professor Mark Csele] {{Webarchive|url=https://web.archive.org/web/20090601213219/http://www.technology.niagarac.on.ca/staff/mcsele/lasers/index.html |date=June 1, 2009 }} [469] => * [https://www.newscientist.com/article/dn13634-powerful-laser-is-brightest-light-in-the-universe.html Powerful laser is 'brightest light in the universe']{{mdash}}The world's most powerful laser as of 2008 might create supernova-like shock waves and possibly even antimatter [470] => * "[http://www.optique-ingenieur.org/en/courses/OPI_ang_M01_C01/co/OPI_ang_M01_C01_web_1.html Laser Fundamentals]" an online course by F. Balembois and S. Forget. [471] => * [https://web.archive.org/web/20081208094614/http://www.irconnect.com/noc/press/pages/news_releases.html?d=154600 Northrop Grumman's Press Release on the Firestrike 15 kW tactical laser product] [472] => * [http://www.laserfest.org/ Website on Lasers 50th anniversary by APS, OSA, SPIE] [473] => * [http://www.advancingthelaser.org/ Advancing the Laser anniversary site by SPIE: Video interviews, open-access articles, posters, DVDs] {{Webarchive|url=https://web.archive.org/web/20210423022457/http://www.advancingthelaser.org/ |date=April 23, 2021 }} [474] => * [http://www.aip.org/history/exhibits/laser/sections/raydevices.html Bright Idea: The First Lasers] {{Webarchive|url=https://web.archive.org/web/20121003143420/http://www.aip.org/history/exhibits/laser/sections/raydevices.html |date=October 3, 2012 }} history of the invention, with audio interview clips. [475] => * [https://nanohub.org/resources/laserdyn Free software for Simulation of random laser dynamics] [476] => * [http://ocw.mit.edu/resources/res-6-006-video-demonstrations-in-lasers-and-optics-spring-2008/ Video Demonstrations in Lasers and Optics] Produced by the Massachusetts Institute of Technology (MIT). Real-time effects are demonstrated in a way that would be difficult to see in a classroom setting. [477] => * [http://ocw.mit.edu/resources/res-6-005-understanding-lasers-and-fiberoptics-spring-2008/laser-fundamentals-i/ MIT Video Lecture: Understanding Lasers and Fiberoptics] [478] => * [http://spie.org/x39914.xml Virtual Museum of Laser History, from the touring exhibit by SPIE] [479] => * [http://www.toutestquantique.fr/#laser website with animations, applications and research about laser and other quantum based phenomena] Universite Paris Sud [480] => [481] => {{Lasers}} [482] => {{Authority control}} [483] => [484] => [[Category:1960 introductions]] [485] => [[Category:Lasers| ]] [486] => [[Category:American inventions]] [487] => [[Category:Articles containing video clips]] [488] => [[Category:Photonics]] [489] => [[Category:Quantum optics]] [490] => [[Category:Russian inventions]] [491] => [[Category:Soviet inventions]] [] => )
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Laser

Laser, short for Light Amplification by Stimulated Emission of Radiation, is a device that emits a concentrated beam of light through the process of optical amplification. Originally conceptualized by Albert Einstein in the early 20th century, lasers have become an integral part of various industries and scientific fields.

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Originally conceptualized by Albert Einstein in the early 20th century, lasers have become an integral part of various industries and scientific fields. This Wikipedia page provides a comprehensive overview of lasers, including their history, principles of operation, types, and applications. It explains how lasers work by stimulating atoms or molecules to emit light, resulting in a coherent and monochromatic beam. The article also covers the different types of lasers, such as solid-state, gas, and semiconductor lasers, discussing their unique characteristics and applications. Furthermore, the page delves into the wide range of applications of lasers in multiple sectors. It highlights their use in telecommunications, medicine (including laser surgery and cosmetic procedures), industry (cutting, welding, and 3D printing), research (spectroscopy and microscopy), and military applications (range finding and target designation). The article emphasizes the importance of safety precautions in handling lasers due to their potential to cause eye damage or skin burns. It outlines the regulations and international standards implemented to ensure their safe use. In addition, the page explores the ongoing research and advancements in laser technology, such as the development of ultrafast lasers, fiber lasers, and laser cooling techniques. It also discusses the potential future applications of lasers, including quantum computing and fusion energy. Overall, the Wikipedia page on lasers provides a comprehensive and informative overview of this vital technology, offering a solid foundation for understanding its history, principles, applications, and future prospects.

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