Editing List of laser applications (section)

==Scientific==

In science, lasers are used in many ways, including:
* A wide variety of [[interferometry|interferometric]] techniques
* [[Raman spectroscopy]]
* [[Laser induced breakdown spectroscopy]]
* [[Atmospheric]] ''[[remote sensing]]''
* Investigating [[nonlinear optics]] [[phenomena]]
* [[Holography|Holographic]] techniques employing lasers also contribute to a number of measurement techniques.
* Laser based [[lidar|lidar (LIght raDAR)]] technology applications in [[geology]], [[seismology]], remote sensing and [[atmospheric physics]].
* Three-dimensional structural modifications and writing inside technological materials.<ref>{{cite journal |title=Laser nanofabrication inside silicon with spatial beam modulation and anisotropic seeding |journal=Nat. Commun. |volume=15 |issue=5786 |year=2024 |doi=10.1038/s41467-024-49303-z|pmc=11252398 }}</ref>
* Lasers have been used aboard spacecraft such as in the [[Cassini-Huygens]] mission.<ref>{{cite web |last1=Wills |first1=Stewart |title=Cassini's Earthbound Partners |url=https://www.osa-opn.org/home/newsroom/2017/september/cassini_s_earthbound_partners/ |website=Optics and Photonics News |publisher=The Optical Society |access-date=7 July 2018 |archive-url=https://web.archive.org/web/20180707201939/https://www.osa-opn.org/home/newsroom/2017/september/cassini_s_earthbound_partners/ |archive-date=7 July 2018 |url-status=live |df=dmy-all }}</ref>
* In [[astronomy]], lasers have been used to create artificial ''[[laser guide star]]s'', used as reference objects for [[adaptive optics]] telescopes.

Lasers may also be indirectly used in [[spectroscopy]] as a micro-sampling system, a technique termed Laser [[ablation]] (LA), which is typically applied to [[ICP-MS]] apparatus resulting in the powerful LA-ICP-MS.

The principles of laser spectroscopy are discussed by Demtröder.<ref>[[W. Demtröder]], Laser Spectroscopy, 3rd Ed. (Springer, 2009)</ref>

===Spectroscopy===
Most types of laser are an inherently pure source of light; they emit near-[[monochromatic]] light with a very well defined range of [[wavelength]]s. By careful design of the laser components, the purity of the laser light (measured as the "[[linewidth]]") can be improved more than the purity of any other light source. This makes the laser a very useful source for [[spectroscopy]]. The high intensity of light that can be achieved in a small, well collimated beam can also be used to induce a nonlinear optical effect in a sample, which makes techniques such as [[Raman spectroscopy]] possible. Other spectroscopic techniques based on lasers can be used to make extremely sensitive detectors of various molecules, able to measure molecular concentrations in the parts-per-10<sup>12</sup> (ppt) level. Due to the high power densities achievable by lasers, beam-induced atomic emission is possible: this technique is termed [[Laser induced breakdown spectroscopy]] (LIBS).

===Heat treatment===
Heat treating with the lasers allows selective surface hardening against wear with little or no distortion of the component. Because this eliminates much part reworking that is currently done, the laser system's capital cost is recovered in a short time. An inert, absorbent coating for laser heat treatment has also been developed that eliminates the fumes generated by conventional paint coatings during the heat-treating process with {{CO2}} laser beams.

One consideration crucial to the success of a heat treatment operation is control of the laser beam irradiance on the part surface. The optimal irradiance distribution is driven by the thermodynamics of the laser-material interaction and by the part geometry.

Typically, irradiances between 500 and 5000 W/cm^2 satisfy the thermodynamic constraints and allow the rapid surface heating and minimal total heat input required. For general heat treatment, a uniform square or rectangular beam is one of the best options. For some special applications or applications where the heat treatment is done on an edge or corner of the part, it may be better to have the irradiance decrease near the edge to prevent melting.

=== Weather ===
Research shows that scientists may one day be able to induce [[rain]] and [[lightning]] storms (as well as micro-manipulating some other weather phenomena) using [[high energy laser]]s. Such a breakthrough could potentially eradicate [[drought]]s, help alleviate weather related [[Disaster|catastrophes]], and allocate weather resources to areas in need.<ref>{{Cite web |url=https://www.express.co.uk/news/science/859871/weather-forecast-lasers-rain-storm-cloud-california |title=California scientists able to control the weather using lasers - www.express.co.uk |date=28 September 2017 |access-date=2018-10-23 |archive-url=https://web.archive.org/web/20181023080204/https://www.express.co.uk/news/science/859871/weather-forecast-lasers-rain-storm-cloud-california |archive-date=2018-10-23 |url-status=live }}</ref><ref>{{Cite web |url=https://www.cnn.com/2015/04/24/tech/laser-cloud-seeding-mci/index.html |title=The man who wants to control the weather with lasers - www.cnn.com |website=[[CNN]] |date=24 April 2015 |access-date=2018-10-23 |archive-url=https://web.archive.org/web/20181023080232/https://www.cnn.com/2015/04/24/tech/laser-cloud-seeding-mci/index.html |archive-date=2018-10-23 |url-status=live }}</ref>

===Lunar laser ranging===
{{Main|Lunar laser ranging experiment}}
When the Apollo astronauts visited the Moon, they planted [[retroreflector]] arrays to make possible the [[Lunar Laser Ranging Experiment]]. Laser beams are focused through large [[telescope]]s on Earth aimed toward the arrays, and the time taken for the beam to be reflected back to Earth measured to determine the distance between the Earth and Moon with high accuracy.

===Photochemistry===
Some laser systems, through the process of [[mode-locking|mode locking]], can produce extremely brief pulses of light - as short as picoseconds or femtoseconds (10<sup>−12</sup> - 10<sup>−15</sup> seconds). Such pulses can be used to initiate and analyze chemical reactions, a technique known as ''photochemistry''. The short pulses can be used to probe the process of the reaction at a very high temporal resolution, allowing the detection of short-lived intermediate molecules. This method is particularly useful in [[biochemistry]], where it is used to analyse details of protein folding and function.

===Laser scanner===
{{Main|Barcode reader}}
Laser barcode scanners are ideal for applications that require high speed reading of linear codes or stacked symbols.

===Laser cooling===
{{Main|Laser cooling}}
A technique that has recent success is ''laser cooling''. This involves [[atom trapping]], a method where a number of atoms are confined in a specially shaped arrangement of [[electric field|electric]] and [[magnetic field]]s. Shining particular wavelengths of light at the ions or atoms slows them down, thus ''cooling'' them. As this process is continued, they all are slowed and have the same energy level, forming an unusual arrangement of matter known as a [[Bose–Einstein condensate]].

=== Nuclear fusion ===
{{Main|Inertial confinement fusion}}

Some of the world's most powerful and complex arrangements of multiple lasers and optical amplifiers are used to produce extremely high intensity pulses of light of extremely short duration, e.g. [[laboratory for laser energetics]], [[National Ignition Facility]], [[GEKKO XII]], [[Nike laser]], [[Laser Mégajoule]], [[HiPER]]. These pulses are arranged such that they impact pellets of [[tritium]]&ndash;[[deuterium]] simultaneously from all directions, hoping that the squeezing effect of the impacts will induce atomic [[nuclear fusion|fusion]] in the pellets. This technique, known as "[[inertial confinement fusion]]", so far has not been able to achieve "breakeven", that is, so far the fusion reaction generates less power than is used to power the lasers, however; experiments at the [[National Ignition Facility]] were able to demonstrate fusion reactions that generate more energy than was contained within the lasers driving the reaction.<ref>{{cite journal |title=Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment |journal=Phys. Rev. Lett. |volume=132 |issue=6 |pages=065102 |doi=10.1103/PhysRevLett.132.065102 }}</ref>

=== Particle acceleration ===
{{Main|Plasma acceleration}}
Powerful lasers producing ultra-short (in the tens of femtoseconds) and ultra-[[Intensity (physics)|intense]] (up to 10<sup>23</sup> W/cm<sup>2</sup>) laser pulses offer much greater acceleration gradients than that of conventional [[Particle accelerator|accelerators]]. This fact is exploited in several [[plasma acceleration]] techniques used for accelerating both [[electron]]s and charged [[ion]]s to high energies.

===Microscopy===
[[Confocal laser scanning microscopy]] and [[Two-photon excitation microscopy]] make use of lasers to obtain blur-free images of thick specimens at various depths.  [[Laser capture microdissection]] use lasers to procure specific cell populations from a tissue section under microscopic visualization.

Additional laser microscopy techniques include harmonic microscopy, four-wave mixing microscopy<ref>{{cite book |editor = Duarte FJ |title=Tunable Laser Applications | edition = 2nd |publisher= [[CRC Press]] |location=Boca Raton |year=2009 |chapter=Chapter 9}}</ref> and interferometric microscopy.<ref>{{cite book |editor = Duarte FJ |title=Tunable Laser Applications | edition = 3rd |publisher= [[CRC Press]] |location=Boca Raton |year=2016 |isbn=9781482261066 | author = Duarte FJ | chapter = Tunable Laser Microscopy| pages =  315–328 }}</ref>