The position and radius at which a Gaussian beam is smallest, usually quoted as the 1/e squared intensity radius w0. On either side the beam grows, slowly within the Rayleigh range and then linearly. Waist size and location set spot size on a workpiece, coupling into fibers and the focusing in nonlinear crystals, so mode-matching calculations always start from it.
Put the waist in the middle of the crystal, not on the front face, or you're throwing away half your conversion.
Also heard as
- waist
- w0
Related terms
Rayleigh range
The distance from a beam's waist to where its cross-sectional area has doubled, a measure of depth of focus.
Gaussian beam
A beam whose intensity falls off from the center as a bell curve, the shape of an ideal single-mode laser.
Divergence
How fast a laser beam spreads with distance far from its waist, given as an angle in milliradians.
M-squared
The beam quality factor: how many times worse a beam focuses and diverges than an ideal Gaussian of the same wavelength.