Transparent nanohybrids of nanocrystalline TiO₂ in PMMA with unique nonlinear optical behavior

PMMA is one of the most versatile polymeric materials for applications in various technological areas including optics and electro-optics. While the current applications of PMMA in optics and electro-optics are limited by their linear optical behavior, we report here in this paper the unique nonlinear optical behavior of nanohybrids consisting of nanocrystalline TiO₂ in PMMA. Transparent thin films of TiO₂-PMMA nanohybrid on substrates were synthesized by in-situ sol-gel and polymerisation, assisted by spin coating. Using titanium isoproproxide (Ti-iP) as the starting material for nanocrystalline titania, together with methyl methacrylate and 3-(trimethoxysilyl)propyl methacrylate, nanohybrids containing up to 80% Ti-iP in PMMA were successfully realized. The resulting nanohybrid thin films coated on quartz substrates are optically transparent and demonstrate large nonlinear optical behavior, with an ultrafast response of <1.5 ps. The highest two-photon absorption coefficient (β) and nonlinear refractive index (n₂) are observed with the nanohybrid thin film of 60 wt% Ti-iP in PMMA, as confirmed by the Z-scan technique.