A simplified model for polycrystalline BaTiO3 nanoresonator for second harmonic generation

Second Harmonic Generation (SHG) has become a critical technique in material characterization, image processing and microscopy. While bulk crystals have been traditionally used for SHG due to their high conversion efficiencies, limited control over radiation properties, delicate phase-matching condition and alignment pose significant challenges. The exploration of nanoscale materials and structures based on dielectric platforms has provided enhanced SHG efficiency and control, but their limited transparency in the visible spectral range and complex fabrication processes hinder broader application. Barium titanate (BaTiO3), a ferroelectric material with spontaneous polarization and nonlinear optical behavior, presents an attractive alternative due to its suitability for nano-imprinting techniques, facilitating scalable production of metasurfaces. In this study, SHG from single polycrystalline BaTiO3 nanocylinders is investigated. Through polarization-dependent experiments, the influence of crystalline domain orientation and arrangements within the nanocylinders on SHG efficiency is characterized. A simplified numerical model to interpret the different polarization-dependent SHG diagrams obtained from nominally identical nanocylinders is developed. The results reveal the significant impact of domain geometry and relative size on SHG characteristics. By understanding the relationship between domain geometry and SHG giving insights for the material characterization and design optimization of BaTiO3 and other polycrystalline nanostructures in nonlinear optical devices.