Titanium Dioxide Metasurface for Vacuum Ultraviolet Third-harmonic Generation

Abstract

Vacuum ultraviolet (VUV) light, in the wavelength regime between 100nm and 200nm, is of long-lasting interest in both academia and industry for its strong photon energy and efficient absorption in most common materials. However, a simple and robust way of VUV light generation remains to be found. In this thesis, I report a titanium dioxide (TiO2) all-dielectric metasurface that enables light generation at 185nm through photonic resonance enhanced third-harmonic generation (THG). Both theoretical analysis and experimental measurements of the metasurface are presented in detail. A multi-step model to calculate generated THG strength is demonstrated. In addition, I include a heat transfer model to analyze the thermal effect of the high input laser power on THG power dependence. A nonlinear signal enhancement factor of 180 compared to an unpatterned TiO2 thin film is reported in the experiment. Finally, the possibility to further enhance the conversion efficiency of the device by using a reflective structure and redesigning the structure geometry through inverse design is also discussed in the simulation aspect.