Nonlinear optical properties in SrTiO3 thin films by pulsed laser deposition

Well-crystallized 250 nm-thick SrTiO3 thin films on fused-quartz substrate were prepared by pulsed laser deposition. The band-gap of SrTiO3 thin film by transmittance spectra is equal to 3.50 eV, larger than 3.22 eV for the bulk crystal. The nonlinear optical properties of the films were examined with picosecond pulses at 1.064 μm excitation. A large two-photon absorption (TPA) with absorption coefficient of 87.7 cm/GW was obtained, larger than 51.7 cm/GW for BaTiO3 thin films. The nonlinear refractive index n2 is equal to 5.7×10−10 esu with a negative sign, larger than 0.267×10−11 esu for bulk SrTiO3. The large TPA is attributed to intermediate energy levels introduced by the grain boundaries, and the optical limiting behaviors stemming from both TPA and negative nonlinear refraction were also discussed.