We investigate the phase-matching of the high harmonics (HHG) driven by the circular Airy-Gaussian beams (CAiGB), which abruptly auto-focus and subsequently propagate without diffraction. The results show that the harmonics corresponding to both short and long quantum paths can be well phase-matched after the focusing point of the CAiGB. Therefore, the effective interaction length of HHG for CAiGB is much longer than that for the conventional Gaussian beams with the same size of the waist. Our numerical simulations reveal that the harmonics continuously gain up to 1 cm of the propagation distance. This work provides a route to enhance the conversion efficiency of HHG by the coherent control of abrupt auto-focusing beams.
High-order harmonic generation (HHG) driven by an abruptly autofocusing circular Airy vortex beam (CAiVB) is investigated here. The autofocusing property of the CAiVB gives HHG a low initial intensity. The slow divergence after focusing provides a long and sufficiently intense region, which is favorable for HHG. Here, we analyze the phase-matching mechanism in detail by plotting the spatial diagram of the coherence length, while simulating HHG driven by the CAiVB carrying distinct orbital angular momentum in a gas medium, as well as the harmonic distributions in the near and far fields.
Phase‐matching of high harmonics with abruptly auto‐focusing ring‐Pearcey–Gaussian beams is investigated. The slowly diffracted propagation after the auto‐focusing of the beams contributes to a slow decrease in both the intensity and the phase with similar trends along the propagation axis. For a specific beam intensity and a harmonic order, the contributions from the atomic and geometric phases can cancel each other within a sufficiently long propagation distance, resulting in the nearly perfect phase‐matching of the harmonic of which the order depends linearly with the beam intensity. The phase‐matching property indicates a dramatic phase‐matching control scenario: one harmonic can be specifically enhanced by adjusting the beam intensity. A numerical simulation is performed to show that the yield of the selected harmonic continuously increases at a distance up to the centimeter range. These findings are helpful for easy tuning and effective generation of the harmonics.
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