Classical Radiation Reaction in Red-Shifted Harmonics

The collision of a finite electromagnetic plane wave with an electron subject to the Landau-Lifshitz radiation reaction force is studied. A locally monochromatic approximation is derived and compared to numerical evaluation of the exact plane wave result. Energy and transverse momentum spectra are calculated, which clearly display the red-shifting of harmonic features due to radiation reaction effects. Simple formulas are presented to predict the shifting of harmonic edges, whose position can be used in experiments as evidence of radiation reaction.