Effect of structure on nonlinear optical properties in CaCu₃Ti₄O₁₂ films

We report the third-order nonlinear optical properties of CaCu₃Ti₄O₁₂ films with different preferred growth orientations on MgO and fused silica substrates. The films have (310)- and (220)-orientation on MgO and fused silica, respectively, due to the lattice-mismatch. Raman spectra further indicate different atom-bonding states in the films. The nonlinear optical measurements show the films possess the same self-defocusing behavior but with different values of nonlinear refraction, and changed signs of nonlinear absorption. The difference of optical nonlinearity in CaCu₃Ti₄O₁₂ films is ascribed to different lattice parameters and intermediate levels induced by structure