Piezoelectric modulation of nonlinear optical response in BaTiO₃ thin film

We study the nonlinear optical response in a strained thin film ferroelectric oxide BaTiO₃ using piezoelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (001) as a variable strain substrate and La-doped SrTiO₃ as a conductive buffer layer. The rotation-anisotropic second harmonic intensity profile shows hysteretic modulation corresponding to the strain variation from the inverse piezoelectric response of the substrate. An enhancement of 15% is observed at 1.2 kV/cm, while a control sample shows negligible change as a function of piezovoltage. Reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and high-resolution scanning transmission electron microscopy reveal the epitaxial interface. X-ray diffraction and piezoresponse force microscopy confirm tetragonal distortion and ferroelectricity of the BaTiO₃ overlayer. Our results suggest a promising route to enhance the performance of nonlinear optical oxides for the development of future nano-opto-mechanical devices.