Laser-assisted electron-ion recombination: Emitted photons' spectra and recollision effects
Abstract We investigate laser-assisted electron-ion recombination with an emphasis on the spectrum of the emitted high-energy photons. A theory that includes the modification of this spectrum due to the recollision of the incident electron and the ion is presented. Numerical results for the soft X-ray differential power spectra both for a monochromatic and a bichromatic laser field are presented and explained using a semi-classical model. For the bichromatic field with frequencies ω and 2ω, the emitted X-ray spectrum is analysed as a function of the relative phase and the possibility of the coherent phase control is shown. We also show that the laser-assisted electron-ion recombination, which includes the rescattering of the electron at the ion before the recombination, is a process complementary to the well-known processes of high-harmonic generation and high-order above-threshold ionization. For low incoming electron energies, the cut-off of the emitted soft X-ray photon energies, including the process of rescattering, is higher than in the case of the direct recombination process. The results obtained are explained using the semi-classical analysis and the three-step scenario.