Large three-photon absorption in Ba0.5Sr0.5TiO3 films studied using Z-scan technique.

Large picosecond nonlinearities in Ba0.5Sr0.5TiO3 thin films, grown at different temperatures in situ on (100) MgO substrates using rf magnetron sputtering technique, were studied using the Z-scan technique. The nonlinear absorption mechanism, studied near 800 nm using ∼2 and 25 ps pulses, switched from reverse saturable absorption type in the films deposited at temperature<600 °C to three-photon absorption (3PA) in the films deposited at temperature>600 °C. The magnitude of the 3PA coefficient was estimated to be ∼10-21 cm3/W2. Two-photon absorption (2PA) was the dominant mechanism recorded with ∼6 ns pulses. The observed behavior is correlated with morphological and crystallographic texture of the films. The linear refractive index and optical band gap of the films have also been calculated and these show a strong dependence on the substrate temperature. [ABSTRACT FROM AUTHOR]