Influence of dynamic core-electron polarization on the structural minimum in high-order harmonics of CO2 molecules

The laser-induced dynamic core-electron polarization (DCEP) was known critical in the ionization of polar molecules such as CO, but less relevant in that of nonpolar ones, such as $\mathrm{CO}{}_{2}$, $\mathrm{N}{}_{2}$, or $\mathrm{O}{}_{2}$. For the harmonic process, the DCEP is proven to play an essential role for the polar molecule CO; it affects the harmonic intensity through the ionization at a specific instant. However, the influence of DCEP on the harmonic process of nonpolar molecules is still questionable. In this paper, we show that DCEP can affect the high-order harmonic generation (HHG) through a different mechanism---suppressing the distortion of the laser field on the highest occupied molecular orbital (HOMO) during the recombination phase, thus partially recovering the HOMO symmetry. Consequently, this shifts and sharpens the minima in the HHG spectra, which arise from the two-center interference. To support our point, we provide reliable numerical simulation by solving the time-dependent Schr\"odinger equation of the coupled $\mathrm{CO}{}_{2}$ molecule-laser field within the single active electron framework. From the minima location, we also extract the internuclear separation O--O of $\mathrm{CO}{}_{2}$, which is more accurate if including the DCEP in the simulation.