Laser-modified electron bremsstrahlung in a Coulomb field

We study spontaneous emission of electromagnetic radiation by an electron with given initial asymptotic momentum in interaction with a Coulomb field and with a homogeneous monochromatic electric field (laser field in dipole approximation). The intense field effects are taken into consideration for the initial and final continuum electron states, by using improved Volkov-Coulomb wave functions, including second-order corrections in the interaction with the electromagnetic field. For the evaluation of the transition amplitudes, the so-called three-δ approximation introduced by Korol [A. V. Korol, J. Phys. B 28, 3873 (1995)] is adopted. The numerical results are presented for a linearly polarized field of frequency of 0.117 eV, intensities up to 10-6 a.u., electron energies in the range 50-500 eV, and incident momentum orthogonal to the laser polarization direction. The study focuses on spontaneous emission accompanied by exchange of a fixed number n=0, ±1,±2 of photons with the external field. Deviations from Born results are shown in several cases. We illustrate in graphs how the spontaneous emission is drastically reduced by the presence of the external field.