Generation of High-Order Harmonics and Novel Attosecond Pulses from N₂-Ar Gas Mixture Driven by a Vortex Orthogonal Two-Color Field

Based on the two-dimensional time-dependent Schrödinger equation, this paper systematically investigates and compares the high-order harmonic generation (HHG) characteristics of N₂ molecules (in a mixed state of HOMO and HOMO-1), Ar atoms (in the ground state), and their gas mixture driven by an orthogonal two-color field and a vortex orthogonal two-color field. The results show that under the orthogonal two-color field, both N₂ molecules and Ar atoms can generate pronounced even-order harmonics, and the gas mixture exhibits significant synergistic enhancement for most harmonic orders in the plateau region. In the vortex orthogonal two-color field, the harmonic intensity of Ar atoms is higher than that of N₂ molecules before the 23rd order, whereas the intensity relationship reverses after the 23rd order. The harmonic spectrum of the gas mixture overall tends to resemble that of the dominant component. Further studies reveal that by optimizing the mixing ratio to N₂: Ar = 1: 9 and adjusting the relative phase, constructive interference can be achieved at specific harmonic orders, thereby effectively enhancing the radiation intensity of the target harmonics. Time-frequency analysis indicates that under the vortex field, short-trajectory electrons dominate the harmonic emission. After synthesizing the 9th–21st harmonics, the gas mixture produces an attosecond pulse with a pulse duration of approximately 506 as and an ellipticity of 0.42, whose overall performance is superior to that of pure N₂ molecules (540 as, 0.23) and pure Ar atoms (480 as, 0.35). Furthermore, after far-field propagation, the annular spatial distribution of the harmonic beam evolves into a purer "donut" structure, while the ellipticity of the attosecond pulse is further improved. These results indicate that the synergistic effect of gas mixtures and vortex light fields can effectively control the spatiotemporal characteristics of high-order harmonics and attosecond pulses, providing a theoretical basis and a feasible approach for developing novel controllable ultrafast light sources.