High-order harmonic generation by double-photoionization accounting for the correlation between continuum electrons

We report systematic analytical and numerical studies of the double-ionization of atoms by strong fields, leading to high-order harmonic generation (HHG). The model properly account for the correlation between the double continuum electrons. Calculations are performed within the frame of non-perturbative fully quantum-mechanical strong-field-approximation approach (SFA). To implement the model, we chose He atom as nonlinear medium. The production of HHG is investigated over a broad range of intensities 7.5×10¹⁴ to 4.5×10¹⁵ W/cm² using Nd:YAG and Ti:Sapph incident lasers. The results are in quite good agreement with the cutoff low. We demonstrate that the length of the plateau grows with the laser intensities. We obtain harmonics up to the order 427th and 479th with Nd:YAG and Ti:Sapph incident lasers, respectively. We show that the nature of the incident laser introduces significant changes in the HHG emission rate. This work confirms the predominance of single-ionization processes during the interaction of He with laser fields.