Editing Ultraviolet (section)

== Artificial sources ==

=== "Black lights" ===
{{multiple image
| direction         = vertical
| width             = 220
| image1            = Two black light fluorescent tubes.jpg
| image2            = Two black light lamps.jpg
| footer            = Two black light fluorescent tubes, showing use. The longer tube is a F15T8/BLB 18&nbsp;inch, 15&nbsp;watt tube, shown in the bottom image in a standard plug-in fluorescent fixture. The shorter is an F8T5/BLB 12&nbsp;inch, 8&nbsp;watt tube, used in a portable battery-powered black light sold as a pet urine detector.
}}

{{Main|Blacklight}}
A ''black light'' lamp emits long-wave UVA radiation and little visible light. Fluorescent black light lamps work similarly to other [[fluorescent lamps]], but use a [[phosphor]] on the inner tube surface which emits UVA radiation instead of visible light. Some lamps use a deep-bluish-purple [[Wood's glass]] optical filter that blocks almost all visible light with wavelengths longer than 400&nbsp;nanometers.<ref>
{{cite web
 |title=Insect-O-Cutor
 |url=http://www.insect-o-cutor.com/ioclibrary/blacklight.pdf
 |url-status=live
 |archive-url=https://web.archive.org/web/20130604215247/http://www.insect-o-cutor.com/ioclibrary/blacklight.pdf
 |archive-date=4 June 2013
}}
</ref> The purple glow given off by these tubes is not the ultraviolet itself, but visible purple light from mercury's 404&nbsp;nm spectral line which escapes being filtered out by the coating. Other black lights use plain glass instead of the more expensive Wood's glass, so they appear light-blue to the eye when operating.{{cn|date=May 2024}}

Incandescent black lights are also produced, using a filter coating on the envelope of an incandescent bulb that absorbs visible light (''see section below''). These are cheaper but very inefficient, emitting only a small fraction of a percent of their power as UV. [[mercury vapor lamp|Mercury-vapor]] black lights in ratings up to 1&nbsp;kW with UV-emitting phosphor and an envelope of [[Wood's glass]] are used for theatrical and concert displays.{{cn|date=May 2024}}

Black lights are used in applications in which extraneous visible light must be minimized; mainly to observe ''[[fluorescence]]'', the colored glow that many substances give off when exposed to UV light. UVA / [[UV-B lamps|UVB emitting bulbs]] are also sold for other special purposes, such as [[tanning lamp]]s and reptile-husbandry.{{cn|date=May 2024}}

===Short-wave ultraviolet lamps===
{{multiple image
| align = right
| direction = vertical
| header =
| image1 = Germicidal Lamp 1.jpg
| caption1 = 9&nbsp;watt germicidal UV bulb, in compact fluorescent (CF) form factor
| image2 = Кварцевая лампа.JPG
| caption2 = Commercial germicidal lamp in butcher shop
| width = 220
}}

Shortwave UV lamps are made using a [[fluorescent lamp]] tube with no phosphor coating, composed of [[fused quartz]] or [[vycor]], since ordinary glass absorbs UVC. These lamps emit ultraviolet light with two peaks in the UVC band at 253.7&nbsp;nm and 185&nbsp;nm due to the [[Mercury (element)|mercury]] within the lamp, as well as some visible light. From 85% to 90% of the UV produced by these lamps is at 253.7&nbsp;nm, whereas only 5–10% is at 185&nbsp;nm.<ref>{{cite book |last1=Rodrigues |first1=Sueli |last2=Fernandes |first2=Fabiano Andre Narciso |title=Advances in Fruit Processing Technologies |date=18 May 2012 |publisher=CRC Press |isbn=978-1-4398-5153-1 |page=5 |url=https://books.google.com/books?id=XyXOBQAAQBAJ |language=en |access-date=22 October 2022 |archive-date=5 March 2023 |archive-url=https://web.archive.org/web/20230305221819/https://books.google.com/books?id=XyXOBQAAQBAJ |url-status=live }}</ref> The fused quartz tube passes the 253.7&nbsp;nm radiation but blocks the 185&nbsp;nm wavelength. Such tubes have two or three times the UVC power of a regular fluorescent lamp tube. These low-pressure lamps have a typical efficiency of approximately 30–40%, meaning that for every 100&nbsp;watts of electricity consumed by the lamp, they will produce approximately 30–40&nbsp;watts of total UV output. They also emit bluish-white visible light, due to mercury's other spectral lines. These "germicidal" lamps are used extensively for disinfection of surfaces in laboratories and food-processing industries.<ref>Minkin, J. L., & Kellerman, A. S. (1966). A bacteriological method of estimating effectiveness of UV germicidal lamps. Public Health Reports, 81(10), 875.</ref>

===Incandescent lamps===
'Black light' [[incandescent lamp]]s are also made from an incandescent light bulb with a filter coating which absorbs most visible light. [[Halogen lamp#Spectrum|Halogen lamps]] with [[fused quartz]] envelopes are used as inexpensive UV light sources in the near UV range, from 400 to 300&nbsp;nm, in some scientific instruments. Due to its [[black-body spectrum]] a filament light bulb is a very inefficient ultraviolet source, emitting only a fraction of a percent of its energy as UV, as explained by the [[black body spectrum]].

===Gas-discharge lamps===
{{Main|Gas-discharge lamp}}
Specialized UV [[gas-discharge lamp]]s containing different gases produce UV radiation at particular spectral lines for scientific purposes. [[Argon]] and [[deuterium arc lamp]]s are often used as stable sources, either windowless or with various windows such as [[magnesium fluoride]].<ref>
{{cite report
 |last1=Klose    |first1=Jules Z.
 |last2=Bridges  |first2=J. Mervin
 |last3=Ott      |first3=William R.
 |date=June 1987
 |title=Radiometric standards in the V‑UV
 |series=NBS Special Publication
 |id=250–3
 |department=NBS Measurement Services
 |publisher=U.S. [[National Institute of Standards and Technology]]
 |url=https://www.nist.gov/calibrations/upload/sp250-3.pdf
 |url-status=live
 |archive-url=https://web.archive.org/web/20160611075213/http://www.nist.gov/calibrations/upload/sp250-3.pdf
 |archive-date=11 June 2016
}}
</ref> These are often the emitting sources in UV spectroscopy equipment for chemical analysis.{{cn|date=May 2024}}

Other UV sources with more continuous emission spectra include [[Xenon flash lamp|xenon arc lamps]] (commonly used as sunlight simulators), [[deuterium arc lamp]]s, [[Xenon arc lamp#Xenon-mercury|mercury-xenon arc lamps]], and [[metal-halide lamp|metal-halide arc lamp]]s.{{cn|date=May 2024}}

The [[excimer lamp]], a UV source developed in the early 2000s, is seeing increasing use in scientific fields. It has the advantages of high-intensity, high efficiency, and operation at a variety of wavelength bands into the vacuum ultraviolet.{{cn|date=May 2024}}

===Ultraviolet LEDs===
[[File:UV LED Fluoresence.jpg|thumb|upright|A 380&nbsp;nanometer UV LED makes some common household items fluoresce.]]
[[Light-emitting diodes]] (LEDs) can be manufactured to emit radiation in the ultraviolet range. In 2019, following significant advances over the preceding five years, UVA LEDs of 365&nbsp;nm and longer wavelength were available, with efficiencies of 50% at 1.0&nbsp;W output. Currently, the most common types of UV LEDs are in 395&nbsp;nm and 365&nbsp;nm wavelengths, both of which are in the UVA spectrum. The rated wavelength is the peak wavelength that the LEDs put out, but light at both higher and lower wavelengths are present.<ref>{{cite journal |last1=Bhattarai |first1=Trailokya |last2=Ebong |first2=Abasifreke |last3=Raja |first3=M.Y.A. |title=A Review of Light-Emitting Diodes and Ultraviolet Light-Emitting Diodes and Their Applications |journal=Photonics |date=May 2024 |volume=11 |issue=6 |page=491 |doi=10.3390/photonics11060491 |doi-access=free |bibcode=2024Photo..11..491B }}</ref>

The cheaper and more common 395&nbsp;nm UV LEDs are much closer to the visible spectrum, and give off a purple color. Other UV LEDs deeper into the spectrum do not emit as much visible light.<ref>{{cite web
 |title=What is the difference between 365&nbsp;nm and 395&nbsp;nm UV LED lights?
 |website=waveformlighting.com
 |url=https://www.waveformlighting.com/tech/what-is-the-difference-between-365-nm-and-395-nm-uv-led-lights
 |access-date=2020-10-27
 |archive-date=22 May 2021
 |archive-url=https://web.archive.org/web/20210522101632/https://www.waveformlighting.com/tech/what-is-the-difference-between-365-nm-and-395-nm-uv-led-lights
 |url-status=live
 }}</ref> LEDs are used for applications such as [[UV curing]] applications, charging glow-in-the-dark objects such as paintings or toys, and lights for detecting counterfeit money and bodily fluids. UV LEDs are also used in digital print applications and inert UV curing environments. As technological advances beginning in the early 2000s have improved their output and efficiency, they have become increasingly viable alternatives to more traditional UV lamps for use in UV curing applications, and the development of new UV LED curing systems for higher-intensity applications is a major subject of research in the field of UV curing technology.<ref>{{cite journal |last1=Patil |first1=Renuka Subhash |last2=Thomas |first2=Jomin |last3=Patil |first3=Mahesh |last4=John |first4=Jacob |title=settings Order Article Reprints Open AccessReview To Shed Light on the UV Curable Coating Technology: Current State of the Art and Perspectives |journal=Journal of Composites Science |date=2023 |volume=7 |issue=12 |pages=513 |doi=10.3390/jcs7120513 |doi-access=free }}</ref>

UVC LEDs are developing rapidly, but may require testing to verify effective disinfection. Citations for large-area disinfection are for non-LED UV sources<ref>
{{cite journal
 |last1=Boyce |first1=J.M.
 |year=2016
 |title=Modern technologies for improving cleaning and disinfection of environmental surfaces in hospitals
 |journal=Antimicrobial Resistance and Infection Control
 |volume=5 |issue=1
 |page=10
 |pmid=27069623 |pmc=4827199 |doi=10.1186/s13756-016-0111-x
|doi-access=free
 }}
</ref> known as [[germicidal lamp]]s.<ref name="Liverpool, UVGI" >
{{cite web
 |title=Ultraviolet germicidal irradiation  |page=3
 |publisher=[[University of Liverpool]]
 |url=https://www.liverpool.ac.uk/media/livacuk/radiation/pdf/UV_germicidal.pdf
 |url-status=dead
 |archive-url=https://web.archive.org/web/20160806185506/https://www.liverpool.ac.uk/media/livacuk/radiation/pdf/UV_germicidal.pdf
 |archive-date=2016-08-06
}}
</ref> Also, they are used as line sources to replace [[deuterium lamp]]s in [[HPLC|liquid chromatography]] instruments.<ref>
{{cite news
 |title=UV‑C LEDs Enhance Chromatography Applications
 |website=GEN Eng News
 |url=http://www.genengnews.com/gen-articles/uvc-leds-enhance-chromatography-applications/5880
 |url-status=live
 |archive-url=https://web.archive.org/web/20161104020423/http://www.genengnews.com/gen-articles/uvc-leds-enhance-chromatography-applications/5880
 |archive-date=4 November 2016
}}
</ref>

===Ultraviolet lasers===
{{main|Excimer laser}}
[[Gas laser]]s, [[laser diode]]s, and [[solid-state laser]]s can be manufactured to emit ultraviolet rays, and lasers are available that cover the entire UV range. The [[nitrogen gas laser]] uses electronic excitation of nitrogen molecules to emit a beam that is mostly UV. The strongest ultraviolet lines are at 337.1&nbsp;nm and 357.6&nbsp;nm in wavelength. Another type of high-power gas lasers are [[excimer laser]]s. They are widely used lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges. Presently, UV [[argon fluoride laser|argon-fluoride]] excimer lasers operating at 193&nbsp;nm are routinely used in [[integrated circuit]] production by [[photolithography]]. The current{{Clarify timeframe|date=June 2020}} wavelength limit of production of coherent UV is about 126&nbsp;nm, characteristic of the Ar<sub>2</sub>* excimer laser.{{cn|date=May 2024}}

Direct UV-emitting laser diodes are available at 375&nbsp;nm.<ref>{{cite web
 | title=UV laser diode: 375&nbsp;nm center wavelength
 | website=Thorlabs
 | location=United States / Germany
 | series=Product Catalog
 | language=en
 | url=http://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=5400
 | access-date=14 December 2014
 | archive-date=15 December 2014
 | archive-url=https://web.archive.org/web/20141215055051/http://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=5400
 | url-status=live
 }}</ref> UV diode-pumped solid state lasers have been demonstrated using [[cerium]]-[[Dopant|doped]] lithium strontium aluminum fluoride crystals (Ce:LiSAF), a process developed in the 1990s at [[Lawrence Livermore National Laboratory]].<ref name="Marshall1996">
{{cite report
 |last = Marshall |first = Chris
 |title = A simple, reliable ultraviolet laser: The Ce:LiSAF
 |publisher = [[Lawrence Livermore National Laboratory]]
 |year = 1996
 |url = https://www.llnl.gov/str/Marshall.html
 |access-date = 2008-01-11  |url-status = dead
 |archive-url = https://web.archive.org/web/20080920155324/https://www.llnl.gov/str/Marshall.html
 |archive-date = 20 September 2008
}}
</ref> Wavelengths shorter than 325&nbsp;nm are commercially generated in [[diode-pumped solid-state laser]]s. Ultraviolet lasers can also be made by applying [[Nonlinear optics|frequency conversion]] to lower-frequency lasers.{{cn|date=May 2024}}

Ultraviolet lasers have applications in industry ([[laser engraving]]), medicine ([[dermatology]], and [[keratectomy]]), chemistry ([[MALDI]]), [[Free Space Optics|free-air secure communications]], computing ([[optical storage]]), and manufacture of integrated circuits.{{cn|date=May 2024}}

===Tunable vacuum ultraviolet (VUV)===
The vacuum ultraviolet (V‑UV) band (100–200&nbsp;nm) can be generated by [[nonlinear optics|non-linear 4&nbsp;wave mixing]] in gases by sum or difference frequency mixing of 2 or more longer wavelength lasers. The generation is generally done in gasses (e.g. krypton, hydrogen which are two-photon resonant near 193&nbsp;nm)<ref name=straussfunk/> or metal vapors (e.g. magnesium). By making one of the lasers tunable, the V‑UV can be tuned. If one of the lasers is resonant with a transition in the gas or vapor then the V‑UV production is intensified. However, resonances also generate wavelength dispersion, and thus the phase matching can limit the tunable range of the 4&nbsp;wave mixing. Difference frequency mixing (i.e., {{nowrap|{{mvar|f}}{{sub|1}} + {{mvar|f}}{{sub|2}} − {{mvar|f}}{{sub|3}}}}) has an advantage over sum frequency mixing because the phase matching can provide greater tuning.<ref name=straussfunk/>

In particular, difference frequency mixing two photons of an {{chem|[[Argon|Ar]]||[[Fluorine|F]]}} (193&nbsp;nm) excimer laser with a tunable visible or near&nbsp;IR laser in hydrogen or krypton provides resonantly enhanced tunable V‑UV covering from 100&nbsp;nm to 200&nbsp;nm.<ref name=straussfunk>{{cite journal
 |last1        = Strauss
 |first1       = C.E.M.
 |last2        = Funk
 |first2       = D.J.
 |year         = 1991
 |title        = Broadly tunable difference-frequency generation of VUV using two-photon resonances in H{{sub|2}} and Kr
 |journal      = Optics Letters
 |volume       = 16
 |issue        = 15
 |pages        = 1192–4
 |doi          = 10.1364/ol.16.001192
 |pmid         = 19776917
 |bibcode      = 1991OptL...16.1192S
 |url          = https://www.osapublishing.org/ol/fulltext.cfm?uri=ol-16-15-1192&id=10705
 |access-date  = 2021-04-11
 |archive-date = 29 May 2024
 |archive-url  = https://web.archive.org/web/20240529134804/https://opg.optica.org/captcha/(S(c0bdkdggeh50wqakxbxp1vlf))/?guid=AEC4DC11-0A8D-48DC-8B6E-84817B588FB2
 |url-status   = live
|url-access= subscription
 }}</ref> Practically, the lack of suitable gas / vapor cell window materials above the [[lithium fluoride]] cut-off wavelength limit the tuning range to longer than about 110&nbsp;nm. Tunable V‑UV wavelengths down to 75&nbsp;nm was achieved using window-free configurations.<ref name="O2Ar">
{{Cite journal
 |last1 = Xiong  |first1 = Bo
 |last2 = Chang  |first2 = Yih-Chung
 |last3 = Ng     |first3 = Cheuk-Yiu
 |year = 2017
 |title = Quantum-state-selected integral cross sections for the charge transfer collision of {{math|{{small|O{{su|b=2|p=+}} (a{{sup|4}} Π {{sub|u 5/2,3/2,1/2,−1/2}}:}}}} {{math|{{small|v{{sup|+}}{{=}}1–2; J{{sup|+}})}}}} {{math|{{small|[ O{{su|b=2|p=+}} (X{{sup|2}} Π {{sub|g 3/2,1/2}}:}}}} {{math|{{small|v{{sup|+}}{{=}}22–23; J{{sup|+}}) ] + Ar}}}} at center-of-mass collision energies of 0.05–10.00&nbsp;eV
 |journal = Phys. Chem. Chem. Phys.
 |volume=19 |issue = 43 |pages=29057–29067
 |bibcode= 2017PCCP...1929057X  |pmid = 28920600 |doi = 10.1039/C7CP04886F
 |url = http://pubs.rsc.org/-/content/articlehtml/2017/cp/c7cp04886f
 |url-status = live
 |archive-url = https://web.archive.org/web/20171115202941/http://pubs.rsc.org/-/content/articlehtml/2017/cp/c7cp04886f
 |archive-date = 15 November 2017
|url-access = subscription
 }}
</ref>

===Plasma and synchrotron sources of extreme UV===
Lasers have been used to indirectly generate non-coherent extreme&nbsp;UV (E‑UV) radiation at 13.5&nbsp;nm for [[extreme ultraviolet lithography]]. The E‑UV is not emitted by the laser, but rather by electron transitions in an extremely hot tin or xenon plasma, which is excited by an excimer laser.<ref>
{{cite web
 |title=E‑UV nudges toward 10&nbsp;nm
 |website=EE Times
 |url=http://www.eetimes.com/document.asp?doc_id=1322626
 |url-status=dead |access-date=26 September 2014
 |archive-url=https://web.archive.org/web/20141015014640/http://www.eetimes.com/document.asp?doc_id=1322626
 |archive-date=15 October 2014
}}
</ref> This technique does not require a synchrotron, yet can produce UV at the edge of the X‑ray spectrum. [[Synchrotron light source]]s can also produce all wavelengths of UV, including those at the boundary of the UV and X‑ray spectra at 10&nbsp;nm.{{cn|date=May 2024}}