Editing Gaussian beam (section)

===Beam waist===<!--Beam waist redirects here-->
{{see also|Beam diameter}}
[[Image:GaussianBeamWaist.svg|thumb|upright=1.5|right|Gaussian beam width {{math|''w''(''z'')}} as a function of the distance {{mvar|z}} along the beam, which forms a [[hyperbola]]. {{math|''w''<sub>0</sub>}}: beam waist; {{mvar|b}}: depth of focus; {{math|''z''<sub>R</sub>}}: [[Rayleigh range]]; {{mvar|Θ}}: total angular spread]]

The shape of a Gaussian beam of a given wavelength {{mvar|λ}} is governed solely by one parameter, the ''beam waist'' {{math|''w''<sub>0</sub>}}. This is a measure of the beam size at the point of its focus ({{math|1=''z'' = 0}} in the above equations) where the beam width {{math|''w''(''z'')}} (as defined above) is the smallest (and likewise where the intensity on-axis ({{math|1=''r'' = 0}}) is the largest). From this parameter the other parameters describing the beam geometry are determined. This includes the [[Rayleigh range]] {{math|''z''<sub>R</sub>}} and asymptotic beam divergence {{mvar|θ}}, as detailed below.