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 for the first time 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 to 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 2E p , and the case of low E p when only infrared photons are produced. Overall accuracy of the classical approach is estimated as very good, although it does not describe resonant processes studied previously by quantum-mechanical methods.

Dipolar focusing in laser-assisted positronium formation

“…A hydrogen atom in an excited state possesses an effective dipole moment leading to a longrange interaction between e + and H(n) [20]. A combination of the dipolar field and a monochromatic laser field can produce the dipolar focusing effect similar to the Coulomb focusing effect in the processes of double photoionization [21,22], electron bremsstrahlung [23], radiative recombination [24], and dissociative recombination [25]. The dipolar focusing effect can be expected to play a role in similar laser-assisted positron scattering processes, such as the process of photorecombination involving positrons and atoms [26].…”