Editing Laser (section)

=== Gas lasers ===
{{Main|Gas laser}}

Following the invention of the HeNe gas laser, many other gas discharges have been found to amplify light coherently.
Gas lasers using many different gases have been built and used for many purposes. The [[helium–neon laser]] (HeNe) can operate at many different wavelengths, however, the vast majority are engineered to lase at 633&nbsp;nm; these relatively low-cost but highly coherent lasers are extremely common in optical research and educational laboratories. Commercial [[Carbon dioxide laser|carbon dioxide (CO<sub>2</sub>) 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&nbsp;μm; such lasers are regularly used in industry for cutting and welding. The efficiency of a CO<sub>2</sub> laser is unusually high: over 30%.<ref>{{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}}</ref> [[Ion laser|Argon-ion]] lasers can operate at several lasing transitions between 351 and 528.7&nbsp;nm. Depending on the optical design one or more of these transitions can be lasing simultaneously; the most commonly used lines are 458&nbsp;nm, 488&nbsp;nm and 514.5&nbsp;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&nbsp;nm.<ref>{{cite web
  |last = Csele
  |first = Mark
  |title = The TEA Nitrogen Gas Laser
  |work = Homebuilt Lasers Page
  |year=2004
  |url = http://www.technology.niagarac.on.ca/people/mcsele/lasers/LasersTEA.htm
  |access-date =September 15, 2007 |archive-url = https://web.archive.org/web/20070911190723/http://www.technology.niagarac.on.ca/people/mcsele/lasers/LasersTEA.htm <!-- Bot retrieved archive --> |archive-date = September 11, 2007}}</ref> Metal ion lasers are gas lasers that generate [[deep ultraviolet]] wavelengths. [[Helium]]-silver (HeAg) 224&nbsp;nm and [[neon]]-copper (NeCu) 248&nbsp;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]]),<ref>{{cite web
  |title = Deep UV Lasers
  |publisher = Photon Systems, Covina, Calif
  |url = http://www.photonsystems.com/pdfs/duv-lasersource.pdf
  |archive-url = https://web.archive.org/web/20070701004933/http://www.photonsystems.com/pdfs/duv-lasersource.pdf
  |archive-date = July 1, 2007
  |access-date =May 27, 2007 }}</ref> making them candidates for use in [[fluorescence]] suppressed [[Raman spectroscopy]].

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

==== Chemical lasers ====

[[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&nbsp;nm) and the [[deuterium fluoride laser]] (3800&nbsp;nm) the reaction is the combination of hydrogen or deuterium gas with combustion products of [[ethylene]] in [[nitrogen trifluoride]].

The first chemical laser was demonstrated in 1965 by Jerome V. V. Kasper and [[George C. Pimentel]] at the University of California, Berkeley. It was a [[hydrogen chloride]] laser operating at 3.7 micrometers.<ref>{{cite journal | last=Gupta | first=Devaryan | title=Laser Technology Applications: A gift to Humanity | journal=International Journal of Applied Research | publisher=AkiNik | volume=1 | issue=7 | date=2016-09-29 | issn=2394-5869 | pages=476–486 | url=https://www.allresearchjournal.com/archives/?year=2015&vol=1&issue=7&part=H&ArticleId=2626 | access-date=2025-03-13}}</ref>

==== Excimer lasers ====

[[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&nbsp;nm), KrCl (222&nbsp;nm), KrF (248&nbsp;nm), XeCl (308&nbsp;nm), and XeF (351&nbsp;nm).<ref>{{cite book
 |first=D. |last=Schuocker |year=1998
 |title=Handbook of the Eurolaser Academy
 |publisher=Springer |isbn=978-0-412-81910-0}}</ref>{{Page missing|date=January 2024}}
The molecular [[fluorine]] laser, emitting at 157&nbsp;nm in the vacuum ultraviolet, is sometimes referred to as an excimer laser; however, this appears to be a misnomer since F<sub>2</sub> is a stable compound.