Two-photon absorption and nonlinear optical properties in undoped and doped ferroelectric thin films

摘要

Barium titanate, Ce-doped barium titanate and La- and Zr-doped lead zirconate titanate thin films were prepared on fused-quartz substrate by laser pulsed deposition. The morphologies and microstructures of the films were examined by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The barium titanate and Ce-doped barium titanate thin films and Zr-doped lead zirconate titanate film are transparent respectively above 322 and 340 nm; while the corresponding optical band gaps are 3.46, 3.48 and 3.46eV. The two-photon absorptions coefficients for barium titanate and Ce-doped barium titanate thin films are very large, as large as 51.7 and 59.3 cm/GW, respectively. Nonlinear refractive index of PLZT film is 1.3 X 10~(-6) esu, much higher than organic polymers, CdS-doped glasses and high density Au-dispersed SiO_2 composite films. The mechanisms for the strong nonlinear optic susceptibilities and large two-photon absorption appeared in barium titanate and Ce-doped barium titanate and Zr-doped lead zirconate titanate film are discussed. On the basis of first principle calculation the nonlinear optic susceptibility and nonlinear two-photon absorption in BaTiO_3 was performed. The theoretical calculations are in good agreement with experimental results.