Editing Laser (section)

=== Semiconductor lasers ===
{{Main|Semiconductor lasers}}

[[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]]]]

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.

Commercial [[laser diode]]s emit at wavelengths from 375&nbsp;nm to 3500&nbsp;nm.<ref>{{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 }}</ref> 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&nbsp;kW, are used in industry for cutting and welding.<ref>{{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}}</ref> 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.

In 2012, [[Nichia]] and [[OSRAM]] developed and manufactured commercial high-power green laser diodes (515/520&nbsp;nm), which compete with traditional diode-pumped solid-state lasers.<ref>{{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}}</ref><ref>{{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}}</ref>

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&nbsp;nm VCSELs are widely available, with 1300&nbsp;nm VCSELs beginning to be commercialized<ref>{{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}}</ref> and 1550&nbsp;nm devices being 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.

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]]s. 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.<ref name="nwls">{{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}}</ref> 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&nbsp;GHz, allowing for on-chip optical signal processing.<ref name="nwpl" /> Another type is a [[Raman laser]], which takes advantage of [[Raman scattering]] to produce a laser from materials such as silicon.

Semiconductor [[quantum dot laser]]s use [[quantum dot]]s as the active laser medium. These lasers exhibit device performance that is closer to gas lasers and avoid some of the disadvantages of traditional semiconductor laser media. Improvements in [[modulation bandwidth]], [[lasing threshold]], [[relative intensity noise]], linewidth enhancement factor and temperature insensitivity have all been observed. The quantum dot active region may also be engineered to operate at different wavelengths by varying dot size and composition. This allows quantum dot lasers to be fabricated to operate at wavelengths previously not possible using semiconductor laser technology.<ref>{{Cite web|url=https://www.fujitsu.com/global/about/resources/news/press-releases/2004/0910-01.html|title=Fujitsu, University of Tokyo Develop World's First 10Gbps Quantum Dot Laser Featuring Breakthrough Temperature-Independent Output - Fujitsu Global}}</ref>