Beam Waist
Definition: location with minimum beam radius
Alternative term: beam focus
German: Strahltaille, Fokus
How to cite the article; suggest additional literature
Author: Dr. Rüdiger Paschotta
The beam waist (or beam focus) of a laser beam is the location along the propagation direction where the beam radius has a minimum. The waist radius is the beam radius at this location.
A small beam waist (more precisely, a beam waist with small waist radius) can be obtained by focusing a laser beam with a lens which has a high numerical aperture, and making sure that the lens aperture is largely filled by the input beam.
For non-circular beams, the position of the beam waist can be different for different transverse directions. This phenomenon is called astigmatism, and it may be generated or removed e.g. by using cylindrical optics.
Simple relations between the beam waist radius and the beam divergence, for example, exist for Gaussian beams.
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See also: laser beams, beam radius, Gaussian beams, The Photonics Spotlight 2007-07-11
and other articles in the category general optics
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