Picosecond pump-probe measurement of bandgap changes in SiO ₂/TiO₂ one-dimensional photonic bandgap structures

A picosecond pump-probe nonlinear optical measurement is performed in SiO₂/TiO₂ one-dimensional photonic bandgap structures fabricated by a solgel method. Both high and low band edges were examined by varying the probe wavelengths and angle tuning was also employed to further clarify the mechanism of a nonlinear optical response. The third-order nonlinear optical response in one-dimensional photonic bandgap structures that comprise TiO₂ films is responsible for the nonlinear optical transmissions at both bandgap edges, with an 8% decrease at the low-energy edge and a 4.5% increase at the high-energy edge for a 355 nm pump intensity of 430 MW/cm ².