A laser is an electronic-optical device that emits coherent light
Radiation. The term "laser" is an acronym for Light Amplification by
stimulated Emission of Radiation.
A typical laser emits light in a narrow, low-divergence
monochromatic (single-coloured, if the laser is operating in the visible
spectrum), beam with a well-defined wavelength. In this respect, laser light is
in sharp contrast with such light sources as the incandescent light bulb, which emits light over a wide area and
over a wide spectrum of wavelengths.
The first working laser was demonstrated on May 16, 1960 by
Theodore Maiman at Hughes Research Laboratories. Since then, lasers have become
a multi-billion dollar industry. The most widespread use of lasers is in optical
storage devices such as compact disc and DVD players, in which the laser (a few
millimeters in size) scans the surface of the disc. Other common applications
of lasers are bar code readers, laser printers and laser pointers.
In industry, lasers are used for cutting steel and other metals
and for inscribing patterns (such as the letters on computer keyboards). Lasers
are also commonly used in various fields in science, especially spectroscopy,
typically because of their well-defined wavelength or short pulse duration in
the case of pulsed lasers. Lasers are used by the military for range finding,
target identification and illumination for weapons delivery. Lasers used in
medicine are used for internal surgery and cosmetic applications.
Design
A laser consists of a gain medium inside a highly reflective
optical cavity, as well as a means to supply energy to the gain medium. The
gain medium is a material with properties that allow it to amplify light by
stimulated emission. In its simplest form, a cavity consists of two mirrors
arranged such that light bounces back and forth, each time passing through the
gain medium. Typically one of the two mirrors,
the output coupler, is partially transparent. The output laser beam is emitted
through this mirror.
Light of a specific wavelength that passes through the gain medium
is amplified (increases in power); the surrounding mirrors ensure that most of
the light makes many passes through the gain medium, being amplified
repeatedly. Part of the light that is between the mirrors (that is, within the
cavity) passes through the partially transparent mirror and escapes as a beam
of light.
The process of supplying the energy required for the amplification
is called pumping. The energy is typically supplied as an electrical current or
as light at a different wavelength. Such light may be provided by a flash lamp
or perhaps another laser. Most practical lasers contain additional elements
that affect properties such as the wavelength of the emitted light and the
shape of the beam.
Although the laser phenomenon was discovered with the help of quantum
physics, it is not essentially more quantum mechanical than other light
sources. The operation of a free electron laser can be explained without
reference to quantum mechanics.
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