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 crystals to make the light with only a 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".
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.
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.
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. Finally, the smallest lasers use semiconductor diodes to produce the light. These are used in electronics.
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 masers and later figured how to make shorter visible wavelengths. 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. 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).
Lasers have found many uses in everyday life as well as in industry. Lasers are found in CD and DVD players, where they read the code from the disk that stores a song or movie. A laser is often used to read the bar codes 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 reflectors left by the Apollo missions. 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.
The first use of lasers in the daily lives of the general population was the supermarket barcode scanner, introduced in 1974. The laserdisc player, introduced in 1978, was the first successful consumer product to include a laser but the compact disc player was the first laser-equipped device to become common, beginning in 1982 followed shortly by laser printers.
Some other uses are:
- Communications: besides fiber-optic communication, lasers are used for free-space optical communication, including laser communication in space.
- Medicine: see below.
- Industry: cutting, welding, material heat treatment, marking parts, non-contact measurement of parts.
- Military: marking targets, guiding munitions, missile defense, electro-optical countermeasures (EOCM), lidar, blinding troops. See below
- Law enforcement: LIDAR traffic enforcement. Lasers are used for latent fingerprint detection in the forensic identification field
- Research: spectroscopy, laser ablation, laser annealing, laser scattering, laser interferometry, lidar, laser capture microdissection, fluorescence microscopy, metrology.
- Commercial products: laser printers, barcode scanners, thermometers, laser pointers, holograms, bubblegrams.
- Entertainment: optical discs, laser lighting displays
In 2004, excluding diode lasers, approximately 131,000 lasers were sold with a value of US$2.19 billion. In the same year, approximately 733 million diode lasers, valued at $3.20 billion, were sold.
Lasers have many uses in medicine, including laser surgery (particularly eye surgery), laser healing, kidney stone treatment, ophthalmoscopy, and cosmetic skin treatments such as acne treatment, cellulite and striae reduction, and hair removal.
Lasers of all but the lowest powers can potentially be used as incapacitating weapons, through their ability to produce temporary or permanent vision loss in varying degrees when aimed at the eyes. The degree, character, and duration of vision impairment caused by eye exposure to laser light varies with the power of the laser, the wavelength(s), the collimation of the beam, the exact orientation of the beam, and the duration of exposure. Lasers of even a fraction of a watt in power can produce immediate, permanent vision loss under certain conditions, making such lasers potential non-lethal but incapacitating weapons. The extreme handicap that laser-induced blindness represents makes the use of lasers even as non-lethal weapons morally controversial, and weapons designed to cause blindness have been banned by the Protocol on Blinding Laser Weapons. Incidents of pilots being exposed to lasers while flying have prompted aviation authorities to implement special procedures to deal with such hazards.
Laser weapons capable of directly damaging or destroying a target in combat are still in the experimental stage.
Throughout the 2000s, the United States Air Force worked on the Boeing YAL-1, an airborne laser mounted in a Boeing 747. It was intended to be used to shoot down incoming ballistic missiles over enemy territory. Ultimately, the project was deemed to be infeasible, and was cancelled in December 2011, with the Boeing YAL-1 prototype being stored and eventually dismantled.
The United States Navy is developing a laser weapon referred to as the Laser Weapon System or LaWS.
United States Air Force laser experiment
A helium–neon laser demonstration at the Kastler-Brossel Laboratory at Univ. Paris 6. The pink-orange glow running through the center of the tube is from the electric discharge which produces incoherent light, just as in a neon tube. This glowing plasma is excited and then acts as the gain medium through which the internal beam passes, as it is reflected between the two mirrors. Laser radiation output through the front mirror can be seen to produce a tiny (about 1 mm in diameter) intense spot on the screen, to the right. Although it is a deep and pure red color, spots of laser light are so intense that cameras are typically overexposed and distort their color.
Mercury Laser Altimeter (MLA) of the MESSENGER spacecraft
Laser application in astronomical adaptive optics imaging
Laser Facts for Kids. Kiddle Encyclopedia.