Why Lasers? Excitation is Enticing!

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What is a LASER?

A laser is a device that emits light (photons) with a specific wavelength or a range of wavelengths over a certain spectrum.

The term LASER stands for "Light Amplification by Stimulated Emission of Radiation".

The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories.

A laser differs from other traditional light sources in that the wavelengths and the waves themselves are synchronized, this is termed spatial coherency and is very important in the function of a laser. Allowing it to be focused on a single place over a long or short distance.

Lasers also have the property of temporal coherence, this allows them to emit light in a very narrow spectrum. For example emit light of a certain wavelength such as a particular color, or in the invisible spectrum such as ultraviolet, xray, infrared and more.

There is one more coherency and that is called temporal coherence, this means lasers can be used to create pulses of specific lengths, all the way down to a femtosecond. (one quadrillionth of a second.)

https://spaceplace.nasa.gov/laser/en/

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Different types - Gas lasers

Following the invention of the helium-neon laser there have been many other gas discharge lasers to be discovered.

The helium-neon laser is able to operate at a variety of different wavelengths.

These relatively low cost are common in research and educational laboratories due to ease of use, adaptability and low cost.

Commercial carbon dioxide lasers can emit many hundreds of watts in a single mode which can be concentrated into a very small area.

This emission is in the thermal infrared and these particular lasers are regularly used in industry for cutting and welding.

A nitrogen transverse electrical discharge in gas laser is a relatively cheap gas laser, often home-built, which produces incoherent UV light.

Metal ion lasers are gas lasers that generate ultraviolet wavelengths.

Helium-silver and neon-copper are two examples of metal ion lasers.

Like all low-pressure gas lasers, the media of these lasers have narrow oscillation linewidths making them candidates for use in fluorescence suppressed spectroscopy.

The oscillation linewidth is a measure of the lasers 'noise' or 'purity', and a perfect laser in this regard will have a single infinitely thin line.

https://www.azooptics.com/Article.aspx?ArticleID=45
https://www.rp-photonics.com/gas_lasers.html
https://community.cadence.com/cadence_blogs_8/b/rf/archive/2008/07/25/please-explain-in-more-practical-less-theoretical-terms-the-concept-of-quot-oscillator-line-width-quot

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Chemical lasers.

Chemical lasers are powered by a chemical reaction releasing a large amount of energy quickly. Such very high power lasers are especially of interest to the military.

However continuous wave high power level chemical lasers fed by streams of gasses have been developed and have some industrial or military applications.

In the hydrogen fluoride laser and the deuterium fluoride laser the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride.

Ethylene is burned in the presence of nitrogen trifluoride in a combustion chamber, which produces free excited fluorine radicals.

The mixture of helium and hydrogen or deuterium is then injected into an exhaust stream via a nozzle.

The deuterium molecules react with the fluorine radicals to produce excited deuterium fluoride.

The excited molecules further undergo stimulated emission in the optical resonating laser region.

Very powerful reaction here, hydrogen fluoride or deuterium fluoride lasers are capable of delivering continuous output power in the megawatt range.

https://www.azooptics.com/Article.aspx?ArticleID=45
http://www.annualreviews.org/doi/abs/10.1146/annurev.pc.34.100183.003013?journalCode=physchem
https://www.google.com/patents/US3706942
https://www.azooptics.com/Article.aspx?ArticleID=480

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Excimer lasers.

Excimer lasers are an exotic gas laser powered by an electric discharge where the medium is an excimer, or more accurately an Exciplex.

An eximer or exciplex is a molecule which can only exist with one atom in an excited electronic state.

Once the molecule transfers its energy to a photon, its atoms are no longer bound together and the molecule disintegrates.

Excimers currently used are all noble gas compounds. Noble gasses are chemically inert (nonreactive at a normal state) and can only form compounds while in an excited state.

Excimer lasers typically operate at ultraviolet wavelengths with applications within the semiconductor industry and eye surgery.

Some excimer molecules include Argon-Fluoride, Krypton-Chlorine, Krypton-Fluorine, Xenon-Chlorine and Xenon-Flourine.

http://www.gigaphoton.com/en/technology/laser/what-is-an-excimer-laser
https://www.coherent.com/lasers/main/excimer-lasers-and-applications

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Solid-state lasers.

Solid-state lasers use a rod made from crystalline or glass material which is doped(impregnated) with ions that provide the required characteristics of the lasing medium.

The first working laser was a ruby solid state laser, so they have been around for a while.

These materials are pumped using a shorter wavelength than the lasing wavelength. Often from a flashtube or from another laser, similar to dumping energy into a device from say an array of batteries or capacitors.

You could potentially line up a number of these lasers and dump energy from one into the next, shortening the length of time the laser was operational and spreading the wavelength to create a high output beam made out of modular parts.

This would allow you to easily replace at portion of the laser if damaged without replacing the entire device at the cost of efficiency with each step added in the chain.

Semiconductor lasers (laser diodes) are typically not referred to as solid-state lasers surprisingly.

Neodymium is a material used to dope various solid-state laser crystals, including yttrium orthovanadate, yttrium lithium fluoride and yttrium aluminum garnet.

All these lasers can produce high powers in the infrared spectrum making them idea for cutting, welding and marking, another use is in spectroscopy and for pumping dye lasers.

Some uses of these lasers include resurfacing joints, removing decay from teeth, vaporizing cancers and pulverizing kidney and gall stones.

Titanium-doped sapphire creates a highly tunable infrared laser commonly used for spectroscopy. It is also notable for use as a laser producing ultra short pulses of high peak power. Read as, good for burning things. Much pew pew.

Thermal limitations in solid-state lasers come about from unconverted power that heats the medium. This heat can cause thermal lensing and reduce the efficiency.

Diode-pumped thin disk lasers overcome this issue by having a medium that is much thinner than the diameter of the pumping beam and this allows for a more uniform temperature in the material.

Thin disk lasers are able to produce high power beams of up to one kilowatt.

http://www.worldoflasers.com/lasertypes-solid.htm
http://www.optique-ingenieur.org/en/courses/OPI_ang_M01_C01/co/Contenu_17.html

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Fiber lasers.

Solid-state lasers or laser amplifiers where the light is guided by an optical fiber are called fiber lasers.

This guiding of light allows extremely long gain regions providing good cooling, fibers have high surface area to volume ratio which allows efficient cooling.

The fiber's waveguiding properties reduce the thermal distortion of the beam. Erbium and ytterbium ions are common in such lasers.

Often the fiber laser is designed as a double-clad fiber, this type of fiber consists of a fiber core, an inner cladding and an outer cladding.

The design of the three layers is chosen so that the fiber core acts as a amplifier (single-mode) for the laser emission while the outer cladding acts as another amplifier (multimode core) for the pump laser. This lets the pump push a large amount of power into and through the active inner core region producing a powerful laser.

Typically used in medicine such as an endoscope or for lasing of internal tissues, metrology such as an atomic clock used in gps measurements to provide better data on weather conditions and cloud formation and the testing of the composition of them, and ultra-precise spectroscopy which is useful for something like astronomy observations.

http://ieeexplore.ieee.org/document/811381/
http://newatlas.com/lockheed-sets-new-record-for-laser-weapon/30655/
http://www.sciencedirect.com/science/article/pii/0030401896003689

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Semiconductor lasers.

Semiconductor lasers are diodes which are electrically pumped.

Reflection from the ends of the crystal form a resonator, interestingly the resonator can be external to the semiconductor.

Commercial laser diodes at Low to medium power are used in laser pointers, laser printers and optical media players such as CD/DVD/MD/LD/BR players.

Laser diodes are also used to optically pump other lasers with high efficiency, stacking together multiple lasers of different types.

The semiconductor lasers can output up to 10 kW and are used in industry for cutting and welding.

External-cavity semiconductor lasers have a semiconductor active medium in a larger cavity.

These particular devices can generate high power outputs with good beam quality, wavelength-tunable radiation, or very short laser pulses allowing for a variety of different applications.

The development of a silicon laser is important in the field of optical computing.

Silicon is the material to use for integrated circuits, and so electronic and silicon laser components could be fabricated on the same chip. (Think multi core cpu with laser interconnects operating in the Gbps range or higher, or low latency high bandwith interconnects on the mainboard for multi chip computing)

There have been some difficulties in regards to this such as silicon has certain properties which block its use as a lasing medium.

However recently teams have produced silicon lasers through methods such as fabricating the lasing material from silicon and other semiconductor materials, such as indium phosphide or gallium arsenide.

These materials allow coherent light to be produced from silicon. These are called hybrid silicon laser.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-14-20-9203
https://www.rp-photonics.com/semiconductor_lasers.html

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Dye lasers.

Dye lasers use an organic dye as the gain medium.

The wide gain spectrum of available dyes or mixtures of dyes, allows these lasers to be highly tunable or to produce very short pulses.

Although these tunable lasers are mainly known in their liquid form, researchers have also demonstrated tunable lasers in configurations utilizing solid-state dye media.

In their most common configuration these solid state dye lasers use doped polymers as the laser media.

https://www.rp-photonics.com/dye_lasers.html

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Free-electron lasers.

Free-electron lasers generate high power emissions that are widely tunable, ranging in wavelength from microwaves through the terahertz range and infrared to the visible spectrum to soft X-rays.

They have the widest frequency range of any laser type. While free electron laser beams share the same optical characteristics as other lasers, such as coherent radiation, the operation is quite different.

Unlike gas, liquid, or solid-state lasers, which rely on bound atomic or molecular states, free electron lasers use a electron beam as the lasing medium, hence the term free-electron.

This tunability allows for virtually any application, at the cost of high power requirements.

https://www-ssrl.slac.stanford.edu/stohr/xfels.pdf
http://www.lightsources.org/what-free-electron-laser

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Applications for lasers.

Lasers range in size from microscopic diode lasers to football field sized lasers used for inertial confinement fusion,
nuclear research and other applications such as launch assists for space craft, cooling devices for research and much more.

Since the laser was developed they have found utility in varied applications in almost every facet of society.

Fiber-optic communication using lasers is a cornerstone in modern communications, allowing services such as the Internet. (Which you are using to read this article!)

The first use of lasers in our daily lives is the supermarket barcode scanner.

The laserdisc player was the first successful consumer product to include a laser. It quickly joined betamax in the not so successful ventures.

However the compact disc player was the first laser-equipped device to become a fixture in most households, followed soon after by laser printers in businesses and homes.

Medicine use such as bloodless surgery, kidney stone treatment, eye surgery and dentistry.

Industry use such as cutting, welding, heat treatment, marking parts and non-contact measurement of parts.

Military use such as marking targets, guiding munitions, alternative to radar aka lidar, blinding troops, range finding and active countermeasures for rockets and missiles.

Law enforcement used in fingerprint detection in the forensic field.

Research use such as spectroscopy, laser ablation, annealing, scattering, interferometry, microdissection, experimental energy sources and more.

Commercial uses such as printers, optical discs, bar-code readers, contact-less thermometers, pointers and holograms.

Laser lighting displays and Laser light shows.

Cosmetic skin treatments such as acne treatment, cellulite reduction, and hair removal.

http://hyperphysics.phy-astr.gsu.edu/hbase/optmod/lasapp.html
https://www.rp-photonics.com/laser_applications.html
https://www.modulight.com/applications-medical/
https://www.modulight.com/applications-display-projection/

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Well, if you made it this far, I tip my hat to you friend. Please let me know if this was informative or educational to you in any way, (or if I made any mistakes which I will hastily fix!) and thank you so much for your time dearest readers.

Much love to you all, and may the world always turn in your favor. <3

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*Edited the article and added the sources I could remember checking in case this does not follow the guidelines for a transformative work. If anyone can shed some light on this it would be great.