Elliptically polarized high-order harmonic generation from the ring-current state of an argon atom in a few-cycle chirped laser field

We theoretically investigate the generation of the elliptically polarized (EP) high-order harmonics from the ring-current state of an argon atom driven by a few-cycle linearly polarized chirped laser pulse. The results show that the harmonic ellipticity is significantly higher in the low-energy region and gradually decreases in the high-energy region of the supercontinuum spectrum, and the higher ellipticity in the low-energy region is attributed to the non-zero orbital angular momentum of the ring-current state. Furthermore, by selectively superposing harmonics from different spectral regions, the ellipticity and duration of the synthesized isolated attosecond pulses can be flexibly controlled. Notably, superposing harmonics from the lower-energy region produce an isolated attosecond pulse with high ellipticity of 0.76, while superposing harmonics from the higher-energy region generate an isolated attosecond pulse with a short duration of 92 as.