New developments in the theory of bremsstrahlung

Abstract We discuss new progress in bremsstrahlung, beyond the predictions previously available. A relativistic code for the calculation of bremsstrahlung in a screened central potential, utilizing an expansion in electron partial waves and photon multipoles, was developed some time ago by Tseng and Pratt [Phys. Rev. A 3 (1971) 100]. For electron bremsstrahlung, unlike for bremsstrahlung in ion-atom collisions, this potential bremsstrahlung contribution generally dominates the atomic or polarizational bremsstrahlung contribution associated with atomic structure, except for radiation of energies comparable to transition energies [M.Y. Amusia and R.H. Pratt, Commun. At. Mol. Phys. 28 (1992) 247]. Predictions from the potential bremsstrahlung calculations are in reasonably good agreement with experiment [R.H. Pratt and I.-J. Feng, in: Atomic Inner Shell Physics, ed. B. Crasemann (Plenum, New York, 1985) p.]. Tabulations are available for both the spectrum and the bremsstrahlung angular distribution [R.H. Pratt, Atom. Data Nucl. Data Tables 20 (1977) 175; L.D. Kissel et al., ibid. 28 (1983) 381]. A major shortcoming has been that the code only obtains the doubly differential cross section, summing over all states of the outgoing scattered electron. No adequate predictions have been available to compare with experimental results for the triply differential cross section, which show substantial disagreement with simpler theory [W. Nakel, in press, 1994]. This problem has recently been remedied [X.M. Tong, C.D. Shaffer and R.H. Pratt, to be published], directly summing numerically the partial wave contributions to the matrix element. In the first cases studied good agreement has been achieved with the experiments. A second shortcoming of the code was its inability to deal with incident electron energies below about 1 keV, needed to study the transition between classical and quantum behavior [L. Kim and R.H. Pratt, Phys. Rev. A 36 (1987) 45]. We discuss recent results in this classical domain. We also review new developments in polarizational bremsstrahlung and two photon bremsstrahlung.