Topic summary
Beam waist
Extracted from the Wikipedia article Gaussian beam.
Beam waist
The shape of a Gaussian beam of a given wavelength λ is governed solely by one parameter, the beam waistw0. This is a measure of the beam size at the point of its focus (z = 0 in the above equations) where the beam width w(z) (as defined above) is the smallest (and likewise where the intensity on-axis (r = 0) is the largest). As noted above, w(z) and w0 are measures of the radius of the beam rather than its diameter, as shown in the diagram.