Description
We investigate signatures of coherent radiation in collisions between a dense charged-particle bunch and an intense laser pulse. We focus on the regime in which the bunch size exceeds the radiation wavelength, a situation where coherent emission is generally expected to be suppressed. However, we demonstrate that coherent radiation can remain strong in directions close to the laser propagation axis.
We analyze in detail the spectrum of the coherent radiation and its dependence on key laser and bunch parameters, including laser intensity and pulse duration, as well as bunch energy, size, shape, and collision angle. We validate our analytical results with three-dimensional particle-in-cell simulations and find very good agreement.
We discuss two experimental strategies for probing coherent radiation: direct detection of the emitted radiation and indirect observation via radiation reaction, i.e., by measuring changes in particle energies and momenta induced by emission. We show that clear signatures of coherent radiation should be observable at existing high-intensity laser facilities.