Elliptically polarized high-order harmonic generation of Ar atom in an intense laser field

High-order harmonic generation (HHG) of Ar atom in an elliptically polarized intense laser field is experimentally investigated in this work. Interestingly, the anomalous ellipticity dependence on the laser ellipticity (epsilon) in the lower-order harmonics is observed, specifically in the 13rd-order, which displays a maximal harmonic intensity at epsilon approximate to 0.1, rather than at epsilon = 0 as expected. This contradicts the general trend of harmonic yield, which typically decreases with the increase of laser ellipticity. In this study, we attribute this phenomenon to the disruption of the symmetry of the wave function by the Coulomb effect, leading to the generation of a harmonic with high ellipticity. This finding provides valuable insights into the behavior of elliptically polarized harmonics and opens up a potential way for exploring new applications in ultrafast spectroscopy and light-matter interactions.