Scattering vector
= Scattering vector
{title2=$\mathbf q=\mathbf k_s-\mathbf k_i$}
The scattered minus incident <wavevector>. In elastic optical scattering, $q=(4\pi n/\lambda_0)\sin(\theta/2)$ for <scattering angle> $\theta$, refractive index $n$ and vacuum <wavelength> $\lambda_0$. A dilute diffusing-particle field correlation decays at rate $Dq^2$ in the single-scattering limit.