Description
Charged particles, interacting with an intense electromagnetic field, emit radiation. Under certain conditions a part of the radiation spectrum is coherent [1-3], which leads to a strong enhancement of radiation friction (RF) – the deceleration of particles due to radiation [3].
We investigate RF in collisions of a laser pulse with a large (at least one linear dimension exceeds the laser wavelength) charged particle bunch and find that for a dense enough bunch ($n\ge 10^{-2} n_c$, where $n_c$ is the plasma critical density) the coherent enhancement increases the effect by orders of magnitude making it observable even at moderate particle energies (of the orders of MeVs) and laser intensities ($I\sim 10^{19}$ W/cm$^2$).
We develop the analytical model for the effect, which provides the average momentum loss of the particle in a bunch as a function of laser pulse intensity and duration as well as of the bunch density, initial energy and size. The predictions of the model are in remarkable agreement with 3-dimensional particle-in-cell simulations. We demonstrate the robustness of our findings with respect to the bunch shape and energy spread.
[1] E. Gelfer, A. Fedotov, O. Klimo, S. Weber, Phys. Rev. Res. 6, L032013 (2024);
[2] E. Gelfer, A. Fedotov, O. Klimo, S. Weber, Matter Radiat. Extremes 9, 024201 (2024);
[3] E. Gelfer, A. Fedotov, M. Malakhov, O. Klimo, S. Weber, arXiv:2502.20290 (2025).
