The laser, acronym for Light Amplification by Stimulated Emission of Radiation, is a device that allows to obtain very intense light beams which, unlike ordinary light (such as, for example, that of the Sun or a common bulb) is monochromatic (all of the same wavelength) and consistent (the photons are all in phase at the same instant). In a common light beam the photons, besides differing in wavelengths, interfering with each other and traveling in different directions and partly dispersed in space. In a coherent light beam, like a laser, you can focus a small amount of energy in a tiny space and the beam of light is easily directional, which makes it very useful for a large number of different applications:
The stimulated radiation emission occurs by administering an amount of energy equal to the difference in energy between two quantum levels, so that the electron is brought to a certain level of energy. When returning to the fundamental state, the electron emits both the photon absorbed and the one due to the jump itself: Photons emitted can in turn stimulate the emission of other electrons present on the same initial energy level. Since the jump is always at the same levels, the photons emitted all have the same energy and the same wavelength, so the radiation that is generated is monochromatic.
The stimulated emission mechanism produces photon emission in phase concordance because the stimulated avalanche emission process takes place at the same time and the resulting beam consists of phase waves, and is said to be a coherent beam.
The structure of a laser is made up of an active material from which light is emitted, a material that can be a crystal, a gas or a solution, and a device designed to provide energy to the atoms of the active material. Normally, the active material is placed between two flat and parallel mirrors, one completely reflective and the other semi-reflective, so that the photons emitted, bouncing on the mirrors, cross over active material several times and help stimulate the most emissions before leaving the semi-reflective mirror. Because the photons are all issued in the same direction, the laser beam is highly collimated.
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