Editing Laser (section)

== History ==

=== Foundations ===

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.<ref name=Einstein1917>{{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 }}</ref> In 1928, [[Rudolf W. Ladenburg]] confirmed the existence of the phenomena of stimulated emission and negative absorption.<ref>{{Cite book |last1=Steen |first1=W. M. |url=https://books.google.com/books?id=gPsq0HHAU4UC&pg=PA11 |title=Laser Material Processing |last2=Steen |first2=William M. |last3=Mazumder |first3=J. |date=2010 |publisher=Springer |isbn=978-1-84996-062-5 |edition=4th |location= |pages=5, 11}}</ref> In 1939, [[Valentin A. Fabrikant]] predicted using stimulated emission to amplify "short" waves.<ref>{{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}}</ref> In 1947, [[Willis&nbsp;E. Lamb]] and R.{{nbsp}}C.{{nbsp}}Retherford found apparent stimulated emission in hydrogen spectra and effected the first demonstration of stimulated emission.<ref>{{Cite book |last1=Steen |first1=W. M. |url=https://books.google.com/books?id=gPsq0HHAU4UC&pg=PA5 |title=Laser Material Processing |last2=Steen |first2=William M. |last3=Mazumder |first3=J. |date=2010 |publisher=Springer |isbn=978-1-84996-062-5 |edition=4th |location= |pages=5}}</ref> 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.<ref>[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.</ref>

=== Maser ===
{{Main|Maser}}

[[File:Aleksandr Prokhorov.jpg|thumb|right|[[Aleksandr Mikhailovich Prokhorov|Aleksandr Prokhorov]]]]

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 in [[Ottawa]], Ontario, Canada.<ref>{{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}}</ref> After this presentation, [[RCA]] asked Weber to give a seminar on this idea, and [[Charles&nbsp;H. Townes]] asked him for a copy of the paper.<ref>{{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}}</ref>

[[File:Charles Townes.jpg|thumb|right|[[Charles H. Townes]]]]

In 1953, Charles H. Townes and graduate students [[James&nbsp;P. Gordon]] and [[Herbert&nbsp;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.<ref>{{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}}</ref> 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.

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.<ref>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.</ref> 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".

=== Laser ===<!--[[WP:MOSHEAD]] notwithstanding-->

{{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]]}}

In April 1957, Japanese engineer [[Jun-ichi Nishizawa]] proposed the concept of a "[[semiconductor laser|semiconductor optical maser]]" in a patent application.<ref name=jqr2>{{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}}</ref> 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]].

[[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. /
Conceive a tube terminated by optically flat / [Sketch of a tube] / partially reflecting parallel mirrors..."]]<!--FAIR USE of Gould notebook 001.jpg: see image description page at File:Gould notebook 001.jpg for rationale -->
Simultaneously, [[Columbia University]] graduate student [[Gordon Gould]] was working on a [[doctoral thesis]] about the energy levels of excited [[thallium]]. Gould and Townes met and talked about radiation [[Emission (electromagnetic radiation)|emission]] as a general subject, but not the specific work they were pursuing. Later, in November 1957, Gould noted his ideas for how a "laser" could be made, including using an open [[resonator]] (an essential laser-device component). His notebook included a diagram of an optically pumped laser. It also contained the first recorded use of the term "laser," an acronym for "light amplification by stimulated emission of radiation," along with suggestions for potential applications of the coherent light beams described.<ref name="pmid36063315"/>

In 1958, Bell Labs filed a patent application for Schawlow and Townes's proposed optical maser; and Schawlow and Townes published a paper with their theoretical calculations in the ''[[Physical Review]]''.<ref>{{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}}</ref><ref>{{cite web |title=Invention of the LASER |website=Invention & Technology Magazine |url=https://www.inventionandtech.com/landmark_landing/80277 |access-date=2024-11-01}}</ref><ref>{{cite web |title=Bell Labs |website=Invention & Technology Magazine |url=https://www.inventionandtech.com/category/inventor/bell-labs |access-date=2024-11-01}}</ref><ref>{{cite web |title=The Back Page |website=American Physical Society |date=2005-05-04 |url=https://www.aps.org/archives/publications/apsnews/201401/backpage.cfm |access-date=2024-11-01}}</ref><ref>{{cite web |title=The Laser Turns 50 (images) |website=CBS News |date=2010-05-15 |url=https://www.cbsnews.com/pictures/the-laser-turns-50-images/ |access-date=2024-11-01}}</ref> That same year, Prokhorov independently proposed using an open resonator, the first published appearance of this idea.

At a conference in 1959, Gordon Gould first published the acronym "LASER" in the paper ''The LASER, Light Amplification by Stimulated Emission of Radiation''.<ref name="Gould1959">{{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}}</ref><ref name="Biographical Memoirs" /> Gould's intention was that different "-ASER" acronyms should be used for different parts of the spectrum: "XASER" for x-rays, "UVASER" for ultraviolet, "RASER" for radio-wave, etc. Instead, the term "LASER" ended up being used for all devices operating at wavelengths shorter than microwaves.

Gould's notes included possible applications for a laser, such as optical telecommunications, [[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 legal fight over the rights to various laser technologies and applications. Gould won his first patent in 1977 for optically pumped laser amplifiers, yet it was not until 1987 that he won his first significant patent infringement claim.<ref>{{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  |at=ch. 35, 47}}</ref> Many aspects of a working laser were patented by different people: the question of just how to assign credit for inventing the laser remains unresolved by historians.<ref>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}}</ref>

On May 16, 1960, Theodore H. Maiman operated the first functioning laser<ref>{{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 }}</ref><ref>{{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}}</ref> at [[Hughes Research Laboratories]], Malibu, California, ahead of several research teams, including those of Townes, at [[Columbia University]], [[Arthur&nbsp;L. Schawlow]], at [[Bell Labs]],<ref>{{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}}</ref>{{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&nbsp;R. Bennett Jr.]], and [[Donald&nbsp;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&nbsp;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&nbsp;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&nbsp;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.

=== Recent innovations ===
[[File:History of laser intensity.svg|thumb|Graph showing the history of maximum laser pulse intensity since 1960]]

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:
* new wavelength bands
* maximum average output power
* maximum peak pulse [[energy]]
* maximum peak pulse [[power (physics)|power]]
* minimum output pulse duration
* minimum linewidth
* maximum power efficiency
* minimum cost

Research on improving these aspects of lasers continues to this day.

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&nbsp;nm.<ref>{{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}}</ref><ref>{{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}}</ref><ref>{{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}}</ref>

In 2017, researchers at the [[Delft University of Technology]] demonstrated an [[Josephson effect#The AC Josephson effect|AC Josephson junction]] microwave laser.<ref>{{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}}</ref> 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]].<ref>{{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}}</ref> 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&nbsp;GHz.<ref name="nwpl">{{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}}</ref>

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.<ref>{{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}}</ref><ref>{{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}}</ref>