Nonlinear geometric metasurfaces are an necessary platform for info encoding and light-field manipulation with extensive purposes in show encryption and past. Enhancing nonlinear conversion effectivity and controlling the nonlinear geometric section are equally essential for sensible use. Just lately, high-Q resonances in nonlocal metasurfaces have proven sturdy light-matter interactions, offering a basis for environment friendly nonlinear conversion. Nevertheless, concurrently reaching excessive effectivity and efficient section management stays a key problem. Right here, primarily based on the precept of geometric section, we effectively understand third-harmonic section management, the place the high-Q resonance corresponds to a magnetic dipole–associated quasi-BIC mode. On the ultra-narrow resonance bandwidth, the electrical discipline enhancement exceeds 50 occasions, with high quality issue over 3000 and excessive stability underneath rotation. A 3rd-harmonic conversion effectivity of the order of 10-3 is achieved at a peak pump density of 100 MW/cm2, outperforming beforehand reported nonlinear geometric metasurfaces. This work holds important potential for on-chip nonlinear info processing and wavefront management requiring sturdy gentle–matter interplay.
