Nonlinear optical behavior of transparent nanohybrids of nanocrystalline TiO₂ in poly(methyl methacrylate) prepared by in situ sol-gel polymerization technique

Nanohybrid thin films consisting of nanocrystalline TiO₂ particles in poly(methyl methacrylate) (PMMA) were successfully synthesized by in-situ sol-gel and polymerization assisted by spin coating. Using titanium isoproproxide (Ti-iP), methyl methacrylate (MMA) and 3-(trimethoxysily) propyl methacrylate (MSMA) as the starting materials, nanohybrids containing up to 60% Ti-iP in PMMA were realized. The resulting nanohybrid thin films coated on quartz substrates are optically transparent and demonstrate nonlinear optical behaviour, where their nonlinear absorption increases with the loading of Ti-iP in PMMA, as confirmed by Z-scan measurements. Using pump-probe technique, these thin films are shown to exhibit an ultrafast relaxation time of ∼ 1.5 picosecond.