For a Gaussian beam, which has 86% of its power within its beam diameter (spot size 2w(adsbygoogle = window.adsbygoogle || []).push({}); _{0}), I've read that beam (angular) divergence is given by

2θ = 4λ/(π[2w_{0}])

Where does this come from? I hate memorizing equations. It makes me feel stupid.

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# Beam divergence derivation

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