High Harmonic Generation in Laser-Assisted Radiative Attachment or Recombination Processes

Resonant enhancements are predicted in cross sections $\sigma_n$ for laser-assisted radiative attachment or electron-ion recombination accompanied by absorption of $n$ laser photons. These enhancements occur for incoming electron energies at which the electron can be attached or recombined by emitting $\mu$ laser photons followed by emission of a spontaneous photon upon absorbing $n+\mu$ laser photons. The close similarity between rescattering plateaus in spectra of resonant attachment/recombination and of high-order harmonic generation is shown based on a general parametrization for $\sigma_n$ and on numerical results for $e-H$ attachment.