One way of quantifying the [Laser beam quality](Laser%20beam%20quality) is with the _beam parameter product._ This is defined in terms of the [divergence half angle](Divergence%20angle.md), $\theta$ as $\mbox{BPP} = w_0\theta$ ^ce77ee where $w_0$ is the [Gaussian beam radius](Gaussian%20beam%20radius.md) at the [beam waist.](Gaussian%20beam%20radius.md#^a9abfb) #Electromagnetism/Optics/waveOptics/GaussianBeamOptics