Laser-induced core-polarization effects in high-order harmonic generation from solids

Under intense laser fields, atoms undergo core polarization, i.e., redistribution of the electron density around the nucleus. We systematically investigate the effect of core polarization on high-order harmonic generation (HHG) from solids using time-dependent density-functional theory in a laser-driven linear chain of atoms. It is shown that the presence of core polarization induces substantial variations in HHG compared with the results with a frozen core. Our study further provides insight into these phenomena by combining an approach that distinguishes the effects of core polarization from different shells and compares the contributions of inner and outer shells. Ultimately, we propose and demonstrate a two-color pump-probe scheme to effectively control the core-polarization effects, specifically by activating inner-shell electrons. This work highlights the significance of multielectron effects for solids and demonstrates the feasibility of manipulating the physical properties of materials through core polarization.