Recoil energy
= Recoil energy
{title2=$E_R=p_R^2/(2m)$}
Recoil energy is the <kinetic energy> gained by an initially stationary atom absorbing a photon of momentum $p_R$. In a standing-wave <optical lattice> of spacing $d$, the photon wavenumber is $\pi/d$, giving $E_R=\hbar^2\pi^2/(2md^2)$.