Laser: Difference between revisions

{{For|the plant used in ancient times as a medicine|Silphium}}

[[File:LASER.jpg|thumb|300x300px|Red (660, 635nm), green (532, 520nm), and blue (445, 405nm) lasers]]

A '''laser''' is a [[machine]] that makes an amplified, single-colour source of light. The beam of light from the laser does not get wider or weaker as most sources of light do. It uses special gases or [[crystal]]s to make the light with only a [[monochrome|single color]]. Then mirrors are used to amplify (make stronger) that colour of light and to make all the light travel in one direction, so it stays as a narrow beam, sometimes called a collimated beam. When pointed at something, this narrow beam makes a single point of light. All of the energy of the light stays in that one narrow beam instead of spreading out like a [[flashlight]] (electric torch).

The word "laser" is an [[acronym]] for "light amplification by stimulated emission of [[radiation]]".

== Mechanism ==

[[File:Laser cutting.JPG|thumb|300x300px|Laser cutting]]

A laser creates light by special actions involving a material called an "[[optical gain medium]]". Energy is put into this material using an 'energy pump'. This can be [[electricity]], another light source, or some other source of energy. The energy makes the material go into what is called an [[excited state]]. This means the [[electrons]] in the material have extra energy, and after a bit of time they will lose that energy. When they lose the energy they will release a [[photon]] (a particle of light). The type of optical gain medium used will change what color ([[wavelength]]) will be produced. Releasing photons is the "stimulated emission of radiation" part of laser.

Many things can radiate light, like a [[light bulb]], but the light will not be organized in one direction and [[phase]]. By using an [[electric field]] to control how the light is created, this light will now be one kind, going in one direction. This is "coherent radiation".

At this point, the light is still weak. The mirrors on either side bounce the light back and forth, and this hits other parts of the optical gain medium, causing those parts to also release photons, generating more light ("light amplification"). When all of the optical gain medium is producing light, this is called saturation and creates a very strong beam of light at a very narrow wavelength, which we would call a laser beam.<ref name="Principles">{{cite book |title=Principles of Instrumental Analysis|coauthors=Skoog, Douglas A., Holler, F. James, Crouch, Stanley R.|year=2007 |publisher=Thomson Brooks/Cole |location=Toronto, ON}}</ref>

==Design==

The light moves through the medium between the two mirrors that reflect the light back and forth between them. One of the mirrors, however, only partially reflects the light, allowing some to escape. The escaping light makes up the laser beam.<ref name="Principles" />

This is a simple design; the type of optical gain medium used usually defines the type of laser. It can be a crystal, examples are ruby and a garnet crystal made of [[yttrium]] and [[aluminum]] with the rare earth metal mixed in. Gases can be used for laser by using [[helium]], [[nitrogen]], [[carbon dioxide]], [[neon]] or others. A [[free-electron laser]] uses a beam of [[electrons]]. Finally, the smallest lasers use [[semiconductor]] [[diode|diodes]] to produce the light. These are used in electronics.<ref name="Principles" />

==History==

[[Albert Einstein]] was the first to have the idea of stimulated emission that could produce a laser. From that point many years were spent to see if the idea worked. At first, people succeeded in making [[maser]]s and later figured how to make shorter visible [[wavelength]]s. It was not until 1959 that the name laser was coined by Gordon Gould in a research paper. The first working laser was put together and operated by [[Theodore Maiman]] at the [[Hughes Research Laboratories]] in 1960.<ref>{{cite book |title=In Search of Schroedinger's Cat|last=Gribbin|first=J|year=1984|publisher=Bantam|location=New York}}</ref> Many people started working on lasers at this time, and the question of who would get the patent for the laser wasn't decided until 1987 (Gould won the rights).<ref>{{citeweb|title=Who Invented the Laser?|url=http://www.aip.org/history/exhibits/laser/sections/whoinvented.html|publisher=American Institute of Physics|accessdate=2013-02-07}}</ref>

== Applications ==

Lasers have found many uses in everyday life as well as in industry. Lasers are found in [[Compact disc player|CD]] and [[DVD player]]s, where they read the code from the disk that stores a song or movie. A laser is often used to read the [[bar code]]s or [[SQR codes]] on things sold in a store, to identify a product and give its price. Lasers are used in medicine, particularly in [[LASIK]] eye surgery, where the laser is used to repair the shape of the [[cornea]]. It is used in chemistry with [[spectroscopy]] to identify materials, to find out what kind of gases, solids or liquids something is made of. Stronger lasers can be used to cut metal.

A laser is even used to measure the distance of the [[Moon]] from [[Earth]] by reflecting off [[reflector]]s left by the [[Apollo program|Apollo]] missions.<ref name="DickeyBender1994">{{cite journal|last1=Dickey|first1=J. O.|last2=Bender|first2=P. L.|last3=Faller|first3=J. E.|last4=Newhall|first4=X X|last5=Ricklefs|first5=R. L.|last6=Ries|first6=J. G.|last7=Shelus|first7=P. J.|last8=Veillet|first8=C.|last9=Whipple|first9=A. L.|last10=Wiant|first10=J. R.|last11=Williams|first11=J. G.|last12=Yoder|first12=C. F.|title=Lunar Laser Ranging: A Continuing Legacy of the Apollo Program|journal=Science|volume=265|issue=5171|year=1994|pages=482–490|issn=0036-8075|doi=10.1126/science.265.5171.482}}</ref> By measuring the time it takes for the light to travel to the Moon and back again we can find out exactly how far away the moon is.

=== Laser pointers ===

Laser pointers are used by people to point at a place on a map or diagram. For example, [[lecture]]rs use them. Also, many people like to play with laser pointers. Some people have pointed them at [[aircraft]]. ThIs is dangerous, and it is also illegal in many countries. People have been arrested and prosecuted for this crime.

==References==

{{reflist}}