TiO2/SiO2 metasurfaces for the enhancement of THG with pump wavelengths in the UV-A

This work demonstrates the potential of amorphous TiO₂-based metasurfaces in nonlinear optics, particularly for VUV light generation via third harmonic generation (THG). Using nanorectangles of TiO₂ on fused silica substrates, we achieve electric anapole excitation in the UV-A range (370 nm) through destructive interference of electric and toroidal dipoles. Simulations confirm angular stability up to 25° and effective light confinement within the nanostructures. Fabrication of amorphous TiO₂ thin films by atomic layer deposition (ALD) revealed that H₂O as an oxidizing agent introduces oxygen vacancies and Ti³⁺ states, increasing optical losses. Transitioning to H₂O₂ improved film quality, aligning with simulations. Experimental validation will assess the material’s bandgap (in the VUV) and optical constants, essential for anapole excitation. These findings establish a pathway for designing TiO₂ metasurfaces with applications in metamaterial optics and nonlinear light generation.