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End Pumping

Definition: a technique of optically pumping a laser medium in a direction along the laser beam

Opposite term: side pumping

German: Endpumpen

Categories: laser devices and laser physics, methods


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End pumping (also sometimes called longitudinal pumping) of lasers and optical amplifiers is a technique of optically pumping a laser gain medium, where the pump light is injected along the laser beam, rather than in a transverse direction (side pumping).

end-pumped laser
Figure 1: Setup of a typical end-pumped solid-state laser.

The geometry of end pumping often allows one to achieve a good spatial overlap between pump and laser radiation. That in turn can have multiple benefits:

For these reasons, most diode-pumped solid-state lasers, particularly those with lower output powers, are end-pumped.

There are also various potential disadvantages of end pumping:

  • Pump light can be injected only from at most two directions, and that may limits the applicable total pump power.
  • Particularly for pumping a long laser crystal with a small beam radius, one requires a pump source with high beam quality, or in combination with a certain level of optical power a high radiance (brightness). Therefore, lamp-pumped lasers, for example, can usually not be end-pumped.
  • The optical intensity and the crystal temperature vary along the beam direction – particularly for unidirectional pumping, but substantially less for bidirectional pumping.

Due to these limitations, end pumping often cannot be used for high-power lasers, and in particular not for lamp-pumped lasers. There are techniques, however, to extend the end pumping concept to fairly high powers; for example, multi-segmented rods (→ composite laser crystals) can be used for better distributing the absorbed power.

See also: optical pumping, lasers, solid-state lasers, side pumping, laser gain media, beam quality, spotlight 2007-04-01

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