I have a question about Thomson scattering from an electron hit by an incident em plane wave. The derivations that I have found all state the same thing. You have an electron in the origin at rest as the initial condition, the incident plane wave is linearly polarized towards z with amplitude E0. The force on the electron is -e*E0cos(ωt). The quadratic mean value of the acceleration is obviously: <a2>=e2E02/2me2 Now plugging that value of the acceleration in the Larmor's formula with obtain the average irradiated power by the electron: P=e2*<a2>/6πε0c3=(8/3)π*re2*I0=σtI0 Now my question about this derivation is the following. If an accelerated electron emits radiation, when we calculate the acceleration value that we put inside the Larmor's formula we can't assume that the only force acting on the electron is -e*E0cos(ωt). We should model the radiating loss with a (usually viscous-like) damping force. We can't get the right acceleration value using a model without losses and the remembering that we have a loss later like it seems to me that authors do in this kind of derivation. Shouldn't the approach be the same of what we use when we want to find the complex permittivity in a dielectric medium where molecules act like oscillating radiating dipoles? In that case losses arising from both radiation scattering and interaction with other molecules are modeled using a damping force.