Generation of near-circularly polarized high-order harmonics in two-color cross-linearly polarized laser fields

We investigate theoretically the ellipticity of the high-order harmonic generation from the molecule H+2 by utilizing two-color cross-linearly polarized laser fields. A significant region of the large ellipticity can be achieved by adjusting the crossing angle and the relative phase between the two laser fields. By controlling the short trajectory, we can obtain the smoother harmonic spectrum. The minimum value observed in the plateau region can be attributed to the two-center interference of the molecule. Furthermore, we investigate the contribution of the two-center interference to the ellipticity of HHG. The underlying physical mechanisms of the ellipticity can be demonstrated by the phase difference and amplitude difference of the x and y components of the harmonics. As a result, we synthesized an isolated attosecond pulse with an ellipticity of 0.98.