Laser

A LASER (Light Amplification by Stimulated Emission of Radiation) is an optical source composed of a resonant optical cavity and a gain medium.

Popular misconceptions

The representation of lasers in popular culture, especially science-fiction or other action movies, as well as their criticism are generally very misleading. For instance, contrary to what appears in movies such as Star Wars, a laser beam is never visible in the vacuum of space. In air the ray can hit dust and any other obstacles in its path and scatter the light giving the appearance of it glowing, in much the same way that a sunbeam glows in a dusty atmosphere. This effect can be intensified to make the beam more visible, for the sake of making a photograph etc, by increasing the particles in the air, for example by spraying air freshner.

Related Topics:
Popular culture - Science-fiction - Star Wars

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Very high intensity beams can be visible in air due to Rayleigh scattering or Raman scattering. With even higher intensity beams, focused to a tight spot, the air can heat up to the point where it becomes a plasma, which would be visible. This would however cause a loud explosion, and will cause a reflection of the ray back into the laser, probably damaging it (depending on the laser design).

Related Topics:
Rayleigh scattering - Raman scattering

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Furthermore, science-fiction film special effects often depict weapon laser beams propagating at only a few metres per second—i.e., slowly enough to see their progress, in a manner reminiscent of conventional tracer ammunition—whereas in reality a laser beam travels at the speed of light, and would be instantly visible along its entire length.

Related Topics:
Special effects - Tracer ammunition - Speed of light

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Some action movies depict security systems using red lasers (and being foiled by the hero, typically using mirrors); the hero may see the path of the beam by sprinkling some white dust in the air. It is actually easier to build infrared laser diodes than visible light laser diodes; therefore such systems have no reason to work in visible light.

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