Theoretical analysis of high-order harmonic generation from the modeled molecular nanoring by an intense mid-infrared laser

High-harmonic generation (HHG) from an idealized theoretical model of the molecular nanoring is numerically investigated by using an intense mid-infrared laser pulse. The resultant nonperturbative HHG exhibits some distinctly different radiation characteristics compared to the traditional gas HHG. Specifically, the harmonic cutoff for a molecular nanoring extends slightly beyond the cutoff law of the gas HHG due to its large spatial scale. The observed extension of the harmonic cutoff in the molecular nanoring can be well explained by a generalized semiclassical three-step model. In the simulation, we also find that the ellipticity dependence of the harmonic intensity for the molecular nanoring is distinguishably weaker than that for the atomic target. The harmonic ellipticities from the molecular nanoring can be continuously controlled by the elliptically polarized laser field within a certain ellipticity range, which offers a promising route to produce ellipticity-tunable harmonic emissions. Our results obtained from the numerical idealized model of the molecular nanoring suggest a potential pathway for achieving atomic-like HHG by a laser pulse only with the intensity on the order of 1012 W/cm2, just like the case of the solid HHG. Compared with the gas HHG triggered generally by the laser pulse with the intensity order of 1014 W/cm2, the novel scheme has the advantages of better accessibility and practicability.