Abstract

The vinylidene fluoride/trifluoroethylene (VDF/TrFE) copolymer is ferroelectric at room temperature, and its Curie temperature is 90°C.¹ The sample consists of a VDF(65)/TrFE(36) copolymer film of a thickness of 4/µm with transparent electrodes InO and ITO on both sides. By varying the voltage between transparent electrodes mentioned above, we observe the typical hysteresis curve of linear polarization P(2ω) vs. poling field E(0) when the incident electric field is E(ω). The linearly polarized Q-switched Nd:YAG laser beam (wavelength 1.06 µm, pulse width 200 ns, and repetition rate 1 kHz) is obliquely incident on the sample mentioned above. The second-harmonic generation reaches its maximum at the incident angle of 50°. Because the sign of the second- order nonlinear-coefficient non- centrosymmetric crystal depends on the crystal orientation and thus the poling field, we can detect the sign of second-harmonic generation by using a nonlinear reference crystal, such as KTP. The X-Y recording of second-harmonic generation or nonlinear polarization from the film versus the poling electric field E(0) is shown for various rates of change poling field. The poled VDF/TrFE copolymer is orthorhombic of class mm2, and the nonlinear coefficients can be changed as a function of the poling field.