  In classical electrodynamics, energy losses due to the emission of
electromagnetic radiation can be accounted for by solving the Landau-Lifshitz
equation of motion. Analytically, this equation is typically solved while
treating each particle independently in an external field; numerically, one
often includes a self-consistent mean field, as seen with particle-in-cell
(PIC) codes. In both cases, interparticle fields from point-like particles are
neglected. By considering the collision of a neutral relativistic
electron-positron bunch with an intense laser pulse, we demonstrate that the
inclusion of interparticle fields can coherently amplify a broad range of
radiated frequencies by orders of magnitude. This corresponds to an amplified
energy loss by particles within the bunch, with interparticle fields that feed
into the radiation reaction force.
