Editing Laser (section)

== Design ==
{{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}}]]

A laser consists of a [[Active laser medium|gain medium]], a mechanism to energize it, and something to provide optical [[feedback]].<ref>{{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}}</ref> 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.{{sfn|Pearsall|2020|p=276=285}}

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.<ref name="pears1">{{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}}</ref>{{Page missing|date=January 2024}}

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.

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''.

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}}