Acronym for light amplification by stimulated emission of radiation. A device that uses certain quantum effects to produce coherent light, which travels with greater efficiency than noncoherent light because the beam diverges only slightly as it travels. Lasers are used in computer technology to transmit data through fiberoptic cables, to read and write data on CD-ROMs, and to place an image on a photosensitive drum in laser printers.
(acronym for light amplification by stimulated emission of radiation) a device for producing a narrow beam of light, capable of traveling over vast distances without dispersion, and of being focused to give enormous power densities (108 watts per cm2 for high-energy lasers). The laser operates on a principle similar to that of the maser (a high-frequency microwave amplifier or oscillator). The uses of lasers include communications (a laser beam can carry much more information than can radio waves), cutting, drilling, welding, satellite tracking, medical and biological research, and surgery.
Laser material
Any substance the majority of whose atoms or molecules can be put into an excited energy state can be used as laser material. Many solid, liquid, and gaseous substances have been used, including synthetic ruby crystal (used for the first extraction of laser light in 1960, and giving a high-power pulsed output) and a helium–neon gas mixture, capable of continuous operation, but at a lower power.
Applications
A blue shortwave laser was developed in Japan in 1988. Its expected application is in random access memory (ram) and compact disc recording, where its shorter wavelength will allow a greater concentration of digital information to be stored and read. A gallium arsenide chip, produced by ibm in 1989, contains the world's smallest lasers in the form of cylinders of semiconductor roughly one-tenth of the thickness of a human hair; a million lasers can fit on a chip 1 cm/2.5 in square.
Sound wave vibrations from the window glass of a room can be picked up by a reflected laser beam. Lasers are also used as entertainment in theaters, concerts, and light shows.
Photon emission
An atom can emit a photon of light (an elementary wave train) if it has somehow gained enough energy to do so; if it has gained this energy it is said to be in an excited state and this can occur, for example, by collision with another atom or by irradiation with light of suitable wavelength. Normally the atom will emit its photon very quickly (in less than 10-6 s) and at random (spontaneous emission), but if a photon of the same wavelength passes while the atom is still in an excited state the atom will emit its photon in phase with the passing photon (stimulated emission). In a laser it is arranged that this process takes place in a manner which causes a rapid buildup of light intensity. The process of providing the atoms with energy is called “pumping”.
Helium and carbon dioxide lasers
The helium–neon laser is the commonest and cheapest kind; it consists of a sealed glass tube containing a mixture of helium and neon gases at low pressure and with mirrors sealed onto the tube at either end. An electrical discharge is passed through the tube from two sealed-in electrodes. The energy of the discharge “pumps” the neon atoms, and photons of wavelength 0.6328 × 10-6 m are emitted (red light). The light bounces to and fro between the mirrors and is amplified at each pass. One of the mirrors is slightly transparent to allow the familiar pencil beam of red light to emerge.
Many hundreds of different materials have now been used to produce laser light in all parts of the spectrum from the ultraviolet to the very long wavelength infrared. Carbon dioxide gas lasers can produce a beam of 100 watts or more power in the infrared (wavelength 10.6 mm) and this has led to an important commercial application, the cutting of material for suits and dresses in hundreds of thicknesses at a time.
Dye lasers, in which complex organic dyes in solution are the lasing material, can be turned to produce light of any chosen wavelength over a range of a sizeable fraction of the visible spectrum.
Laser coherence
Laser light is very coherent and it can be used to demonstrate a variety of interference effects conveniently; it is used for holography and for accurate length measurement by interferometry. On account of its coherence, laser light can be accurately collimated; if a collimated beam 1 m in diameter is made it will spread by diffraction at an angle much less than 1˛ of arc. This has made it possible to send laser pulses to the moon; by detecting the pulses reflected back from mirrors placed on the moon very accurate measurements of the moon’s distance can be made. Quite different applications are for concentrated heat in surgery and welding, and for many purposes in pure science. Lasers can be made to produce very short pulses of light (10-11 s) with very intense peak power (1014 watts) and such pulses are a possible means for initiating the fusion of light elements to produce energy, in the same way that the energy of the Sun is produced.
Light Amplification by Stimulated Emission of Radiation; produces an intense monochromatic beam of coherent light; SYN. optical maser. + prikaži više