EQUINOX GRAPHICS / SCIENCE PHOTO LIBRARY EQUINOX GRAPHICS / SCIENCE PHOTO LIBRARY
Animation showing how a laser works. On the right is the laser equipment, consisting of a gain medium (cylinder) capped by two mirrors, the one on the right end being partially transparent. These components make up the laser's optical cavity. Behind that is the pumping device, which provides energy to the gain medium, seen as flashes of light. On the left of the animation is a diagram showing the states of the atoms in the gain medium (seen as blue dots in the medium and on the diagram). Initially these are all in the ground (low energy) state. A flash from the pump raises some into the excited state. When more atoms are excited than ground, the system is said to be in a population inversion. When atoms fall back to the ground state they emit photons (red). In a population inversion, these are more likely to strike other excited atoms, causing a phemonenon called stimulated emission. When this occurs, the atom emits two photos that have the same phase, polarisation, frequency and direction of travel. As this happens more frequently, more of the photons become the same as each other, a process called optical amplification. More pumping increases the number of these photons yet further, and some escape from the optical cavity through the partially transparent mirror. These photons form the laser beam, and each photon has the same phase, frequency and polarisation. The word laser originated as an acronym for light amplification by stimulated emission of radiation . See clip K002 8520 for a detailed animation of stimulated emission.
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