= Thomson cross-section
{c}
{title2=$\sigma_T=q^4/(6\pi\epsilon_0^2m^2c^4)$}
A free nonrelativistic charge driven by a weak <plane electromagnetic wave> has peak <acceleration> $|q|E_0/m$. Its time-averaged <Larmor formula> <power> is $q^4E_0^2/(12\pi\epsilon_0m^2c^3)$. Divide by incident <light intensity> $\epsilon_0cE_0^2/2$ to obtain the displayed <cross section>, independent of <frequency>. For an <Electron>, it is $8\pi r_e^2/3$. The approximation assumes negligible <Compton recoil kinematics> and small driven <velocity> compared with the <speed of light>.
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