Classical theory of laser-assisted spontaneous bremsstrahlung

Abstract

We study the process of laser-assisted spontaneous electron bremsstrahlung by running classical trajectories in a combined Coulomb and laser (ac) fields. Due to chaotic scattering in the combined Coulomb and ac fields, the radiation probability as a function of the impact parameter and the constant phase of the laser field exhibits fractal structures. However, these structures are smeared out when the cross section is integrated over the impact parameter and averaged over the phase. We analyze the role of different types of orbits, including the trapped orbits, and the dependence of the radiation probability on the impact parameter and the initial phase of the ac field. We show that, at low incident electron kinetic energy, the Coulomb focusing leads to a substantial extension of the range of impact parameters contributing to the bremsstrahlung cross section and results in a substantial increase (by one to two orders of magnitude) of the cross section as compared with the pure Coulomb case. As examples, we discuss the case of relatively high ponderomotive energy ${E}_{p}$ when we obtain an efficient production of photons with frequencies up to $2{E}_{p}$, and the case of low ${E}_{p}$ when only infrared photons are produced. Overall accuracy of the classical approach is estimated to be very good, although it does not describe resonant processes studied previously by quantum-mechanical methods.