Responses To Terahertz Electric Field Of Three Typical Ferroelectric Thin Films

The interaction between terahertz waves and materials is the current research focus which has aroused great amount of attention. However, there is few research on the interaction process between terahertz waves and ferroelectric materials at present. This paper mainly studies the responses of three typical ferroelectric thin films to terahertz electric field, such as the absorption characteristics of BiFeO₃?BFO? polycrystalline powders in the terahertz frequency range, the terahertz electro-optic properties of PbZr_0.52Ti_0.48O₃?PZT? and BaTiO₃?BTO? ferroelectric thin films.We prepare BFO polycrystalline powders by the sol-gel method and study its material properties and absorption characteristics in the terahertz frequency range with a home-built terahertz time-domain spectroscopy?THz-TDS?. We find that there are five distinct absorption peaks at 1.48 THz?2.16THz?2.78THz?3.35 THz and 3.79 THz in the sample respectively. We analyze the characteristics of the absorption peaks by the crystal lattice vibration selective absorption principle and the pseudo-harmonic dielectric model. We also find BFO exists obvious optical rotation activity in the terahertz range.We prepare PZT and BTO epitaxial ferroelectric films and study their material properties and electro-optic effects in the terahertz band by measuring birefringence induced by the electric field with the polarization-resolved THz-TDS. A linear response of PZT film with the linear electro-optic coefficient r_c=6.73×10^-11 m/V, and a quadratic response of BTO film with the second-order electro-optic coefficient R_c=1.42 × 10^-17m²/V², are observed at the frequency of 1 THz under the applied static electric field less than 80 kV/cm. The calculation of rc and Rc based on the Landau-Devonshire free energy theory explains the different electro-optic responses of PZT and BTO well.