B. Böning,
and S. Fritzsche
Steering the longitudinal photoelectron momentum in the above-threshold ionization with two not-quite-collinear laser beams
Phys. Rev. A, 106 :043102 (October 2022)
Steering the longitudinal photoelectron momentum in the above-threshold ionization with two not-quite-collinear laser beams
Phys. Rev. A, 106 :043102 (October 2022)
Abstract:
Strong-field atomic processes, driven by long-wavelength laser beams, are known to be affected by magnetic forces. In such beams, the Lorentz force pushes the photoelectrons along the beam direction and prevents their rescattering or recombination with the parent ions. In high-order harmonic generation (HHG), therefore, the yield of energetic photons is markedly suppressed, rendering x-ray radiation sources from high harmonics so far impractical. To compensate these magnetic forces and to reenable HHG at long wavelengths, a setup of two not quite collinear beams has been suggested recently but not much analyzed beyond classical arguments and with respect to accessible laser parameters. Using the nondipole strong-field approximation, we here investigate when the longitudinal momentum of the photoelectrons vanishes and how this noncollinear setup explicitly depends on the wavelength and intensity of the driving beams. We also demonstrate that an optimal crossing angle delta 0 between these beams always exists for which the fraction of the returning electrons is maximized. This rather simple steering of the longitudinal momentum will allow an efficient HHG with driving beams deep in the midinfrared.