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Technically, the term laser is an acronym for "photoamplification by stimulated emission of radiation," but the term has become so common that it is no longer capitalized. Radiation is the light emitted by a laser. The human eye can or cannot see this light. Technically, only some lasers use optical amplification, but the term laser is monochromatic (all colors or wavelengths) coherent (similar enough for a light wave to travel in one direction). It will continue to be used for devices that generate radiation.

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There are laser media, energy sources, and resonators. A laser medium is a material that can be excited (excited) to a higher energy state by an energy source (light, electricity, etc.). After pumping, the laser medium can emit energy as monochromatic radiation. The resonator is the area where the emitted energy can be stored before it is emitted. The basic cavity is a pair of mirrors on either side of the laser medium. The mirror is completely reflected, so all light reflected by the mirror is reflected back to the blue laser pointer. The other is partially reflected, so some of the light that hits it is reflected back into the laser medium, and some light passes through the medium and exits the laser. A pair of mirrors reflect light back and forth in the laser medium and align it in one direction to create light coherence.

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