Predictable third harmonic generation in GaAs metasurfaces through group theory inverse design of meta-atoms

Here, we report the group theory-based inverse design of meta-atoms for a dielectric metasurface in GaAs with predictable optical linear response and third harmonic generation (THG). Six sharp Fano resonances have been observed with a corresponding polarization dependence as predicted by group theory and the meta-atom's symmetry in the D_2h point group. THG has been observed for two modes under x-polarization excitation and one mode for y-polarization, in agreement with theoretical symmetry predictions. The polarization-dependent THG aspect ratio was observed to reach as high as 10⁸. Through strategic structural or symmetry-preserving perturbations, it was shown that the THG can be enhanced or reduced by a factor of 7. The highest THG conversion efficiency was estimated to be 3.1 × 10^-7 at the pump intensity of 1.51 MW/cm². This high THG conversion efficiency indicates that our group theory approach to modal engineering opens a new path, to the best of our knowledge, toward optical nonlinearity tuning in dielectric metasurfaces.