Bremsstrahlung Regge-type representation

We report a new approach to describe the features of the bremsstrahlung process in electron-atom interaction. The method employs a modification of the Watson transform. We rewrite the partial wave sum in the form of a contour integral in the complex l-plane and we identify contributions due to particular singularities of the elastic scattering S-matrix considered as a function of complex angular momenta. The behavior of the trajectories of these poles, known as Regge poles, as a function of electron energy, exhibits common features for a broad class of potentials, making the representation useful for description of the general features of the bremsstrahlung cross section. We demonstrate that the extent of classical-quantum correspondence for free-free radiative transitions can be assessed using this representation.