Enhancing circularly polarized XUV vortices from bicircular Laguerre-Gaussian fields.

In this work, we theoretically study the generation of circularly polarized XUV vortices from high harmonic generation driven by bicircular Laguerre-Gaussian (LG) fields with different frequency ratios, by using the strong-field approximation theory. Our simulation shows that the amplitude of the generated vortices from the ω-3ω bicircular LG field is about one order of magnitude larger than that from the ω-2ω field, irrespective of the harmonic order and the orbital angular momentum of the bicircular driving fields. Our analysis shows that the great increase of the vortex amplitude for the ω-3ω field originates from the harmonic enhancement of a single atom. Furthermore, in terms of quantum-orbit theory, the underlying physics of the harmonic enhancement of the single atom for the ω-3ω field is revealed. Our work provides a simple and robust method to increase the amplitude of the circularly polarized XUV vortices.