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Photons

Lasers and holograms use the strange behaviour of photons.

Photons of light can behave both like a wave and like a particle. This is described by the quantum theory of light developed by scientists such as Erwin Schrödinger and Richard Feynman.

The quantum theory of light is needed when studying how light interacts with matter. Light is emitted when atoms convert some spare energy into a photon of light. Normally a bunch of atoms will emit photons randomly, producing different kinds of photons travelling in different directions.

Lasers create identical photons of light, which makes laser light special.

Laser light:

  • is a single colour
  • does not spread out very much

The word laser stands for Light Amplification by the Stimulated Emission of Radiation. (Stimulated emission is the process in which identical photons are created. 'Normal' light is produced by a process called spontaneous emission.)

Lasers are used in compact disc players, barcode scanners and surveying equipment, as well as providing spectacular lighting effects. None of this would be possible without our modern, quantum, theory of light.


Feynman
magnifyRichard Feynman


Laser
magnifyLaser


Photons in a laser
magnifyPhotons in a laser
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