Radiation for laser-driven rescattering near the ultimate high-energy cutoff: The single-atom response and bremsstrahlung limit

Abstract

The discovery of laser-driven rescattering and high harmonic radiation out to a maximum photon energy of 3.17 times the ponderomotive energy laid the groundwork for attosecond pulse generation and coherent x rays. As the laser field drives the interaction to higher energies, relativity and the Lorentz force from the laser magnetic field enter into the dynamics. Recent studies of laser rescattering have included these effects to give a quantitative description of rescattering dynamics in the high-energy limit, i.e., recollision energies of order 1,000 hartree (27 keV). In this high-energy limit, we treat the emitted high harmonic radiation from rescattering as a bremsstrahlung process. We find the highest-energy photons in the radiated energy spectra follow the rescattering electron energy near the ultimate cutoff. The effective charge from the ion core shielding does not affect the radiation yield at cutoff; however, the overall energy radiated does scale quadratically with the atomic number of the parent ion.