Optical and Nonlinear Optical Response of Light Sensor Thin Films

For potential ultrafast optical sensor application, both VO2 thin films and nanocomposite crystal-Si enriched SiO2 thin films grown on fused quartz substrates were successfully prepared using pulsed laser deposition (PLD) and RF co-sputtering techniques. In photoluminescence (PL) measurement c-Si/SiO2 film contains nanoparticles of crystal Si exhibits strong red emission with the band maximum ranging from 580 to 750 nm. With ultrashort pulsed laser excitation all films show extremely intense and ultrafast nonlinear optical (NLO) response. The recorded holography from all these thin films in a degenerate-four-wave-mixing configuration shows extremely large third-order response. For VO2 thin films, an optically induced semiconductor-tometal phase transition (PT) immediately occurred upon laser excitation. it accompanied. It turns out that the fast excited state dynamics was responsible to the induced PT. For cSi/SiO2 film, its NLO response comes from the contribution of charge carriers created by laser excitation in conduction band of the c-Si nanoparticles. It was verified by introducing Eu which is often used as a probe sensing the environment variations. It turns out that the entire excited state dynamical process associated with the creation, movement and trapping of the charge carriers has a characteristic 500 ps duration.