Laser light is a type of stimulated emission of radiation.
Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers
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A laser beam used for welding
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A helium–neon laser demonstration. The glow running through the center of the tube is an electric discharge. This glowing plasma is the gain medium for the laser. The laser produces a tiny, intense spot on the screen to the right. The center of the spot appears white because the image is overexposed there.
Spectrum of a helium–neon laser. The actual bandwidth is much narrower than shown; the spectrum is limited by the measuring apparatus.
Lidar measurements of lunar topography made by Clementine mission.
Laserlink point to point optical wireless network
Mercury Laser Altimeter (MLA) of the MESSENGER spacecraft
Aleksandr Prokhorov
Charles H. Townes
LASER notebook: First page of the notebook wherein Gordon Gould coined the acronym LASER, and described the elements required to construct one. Manuscript text: "Some rough calculations on the feasibility / of a LASER: Light Amplification by Stimulated / Emission of Radiation. /
Conceive a tube terminated by optically flat / [Sketch of a tube] / partially reflecting parallel mirrors..."
Graph showing the history of maximum laser pulse intensity throughout the past 40 years.
Wavelengths of commercially available lasers. Laser types with distinct laser lines are shown above the wavelength bar, while below are shown lasers that can emit in a wavelength range. The color codifies the type of laser material (see the figure description for more details).
A 50 W FASOR, based on a Nd:YAG laser, used at the Starfire Optical Range
A 5.6 mm 'closed can' commercial laser diode, such as those used in a CD or DVD player
Close-up of a table-top dye laser based on Rhodamine 6G
The free-electron laser FELIX at the FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein
Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other high energy density physics experiments.
The US–Israeli Tactical High Energy weapon has been used to shoot down rockets and artillery shells.
Laser application in astronomical adaptive optics imaging

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

- Laser

Amplified spontaneous emission (ASE) or superluminescence is light, produced by spontaneous emission, that has been optically amplified by the process of stimulated emission in a gain medium.

- Amplified spontaneous emission

ASE is produced when a laser gain medium is pumped to produce a population inversion.

- Amplified spontaneous emission

Such a gain medium, along with an optical resonator, is at the heart of a laser or maser.

- Stimulated emission

Lacking a feedback mechanism, laser amplifiers and superluminescent sources also function on the basis of stimulated emission.

- Stimulated emission

For lasing media with extremely high gain, so-called superluminescence, it is possible for light to be sufficiently amplified in a single pass through the gain medium without requiring a resonator.

- Laser
Laser light is a type of stimulated emission of radiation.

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Optical amplifiers are used to create laser guide stars which provide feedback to the adaptive optics control systems which dynamically adjust the shape of the mirrors in the largest astronomical telescopes.

Optical amplifier

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Device that amplifies an optical signal directly, without the need to first convert it to an electrical signal.

Device that amplifies an optical signal directly, without the need to first convert it to an electrical signal.

Optical amplifiers are used to create laser guide stars which provide feedback to the adaptive optics control systems which dynamically adjust the shape of the mirrors in the largest astronomical telescopes.
Schematic diagram of a simple Doped Fiber Amplifier

An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback from the cavity is suppressed.

In doped fiber amplifiers and bulk lasers, stimulated emission in the amplifier's gain medium causes amplification of incoming light.

The principal source of noise in DFAs is Amplified Spontaneous Emission (ASE), which has a spectrum approximately the same as the gain spectrum of the amplifier.