(a) Schematic illustration of dielectric constant perturbation and enhanced THG. (b, c) The electric field distributions of the FF and TH on the unit cell cross-section under QBIC resonance frequency. (c) Relationship between the reflection spectrum and THG conversion efficiency as a function of pump light frequency near the QBIC resonance frequency. (e) The dependence of THG power on the polarization angle of pump light. (f) The double-logarithmic plot of THG power versus FF pump power. The fitting curve confirming the cubic relationship of TH optical effect.