Jumpei Hayashi

Deformable Mirror for Mechanical Q-Switching of Laser-Diode-Pumped Microchip Laser

A piezoelectrically deformable output-mirror was used for the mechanical Q-switching of a laser-diode-pumped Nd3+:YVO4 microchip laser. A unimorph structure consisting of a piezoelectric polymer and a polymeric multilayered mirror on a flexible polymer substrate was vibrated to periodically change the laser-cavity loss under the application of an AC voltage of 250 V. It yielded Q-switched pulses with a duration of 16 ns at a repetition rate of 1.338 kHz for a pump power of 284 mW and a cavity length of 16 mm. The average power and peak power were 1.1 mW and 52 W, respectively.

Relaxor Characteristics of BaTiO3-Bi(Mg1/2Ti1/2)O3 Ceramics

Relaxor characteristics of (1-x)BaTiO3-xBi(Mg1/2Ti1/2)O3 (x=0.1–0.7) ceramics were investigated. Microstructural observation showed second phases and no domain structure for the sample with x=0.6. Deviation from the Curie-Weiss behavior was found in temperature dependence of the inverse permittivity for all the samples. The stronger dielectric dispersion was found for x=0.6 and 0.7 and they were described by the Vogel-Fulcher relationship. The temperature dependence of the remanent polarization and coercive field indicated the freezing temperature was 100~150°C for x=0.6. The strong dielectric dispersion of x=0.6 is believed to be induced by the structural disorder due to the second phases.

Anisotropic Polarization Switching in Tungsten Bronze Ferroelectrics in Binary (Bi1/2Na1/2)Nb2O6–BaNb2O6 System

Randomly oriented (1-x)BaNb2O6–x(Bi1/2Na1/2)Nb2O6 ceramics were prepared by conventional solid state sintering. The ceramics (0.2≤x≤0.7) sintered at 1250 °C consisted of a single phase of a tungsten bronze structure, while the end-member materials did not crystallize into the tungsten bronze structure. The crystal systems of tungsten bronze phases were orthorhombic for 0.2≤x≤0.25 and tetragonal for 0.3≤x≤0.7. The temperatures for the maximum dielectric constant (Tm) measured for orthorhombic crystals were 300 and 190 °C for x=0.2 and 0.25, respectively, and showed no frequency dispersion. However, the Tm for tetragonal crystals was suppressed below 160 °C and showed an obvious frequency dispersion. To evaluate the orientation of spontaneous polarization, (001)- and (hk0)-oriented fiber-textured ceramics were prepared for x=0.2, 0.25, and 0.3 by slip casting under a strong magnetic field. Clear hysteresis loops of polarization–electric field were observed for (001)-oriented orthorhombic ceramics (x=0.2 and 0.25) at room temperature, while the polarization induced in the (hk0)-oriented or tetragonal ceramics (x=0.3) varied proportionally to the external electric field. It was concluded that the tungsten bronze crystals, (1-x)BaNb2O6–x(Bi1/2Na1/2)Nb2O6 (x=0.2 and 0.25), are ferroelectric at room temperature with the spontaneous polarization parallel to the c-axis.

Microstructure and Piezoelectric Properties of BaTiO3-Bi(Mg1/2Ti1/2)O3-BiFeO3 Ceramics

Barium titanate (BaTiO3, BT)-bismuth magnesium titanate (Bi (Mg1/2Ti1/2)O3, BMT)-bismuth ferrite (BiFeO3, BF) solid solution ceramics were prepared using a conventional solidstate synthesis, and their piezoelectric properties and microstructure were investigated. Strain electric field curves of the 0.3BT-0.1BMT-0.6BF ceramics with a single perovskite phase were ferroelectric butterfly-like curves. A strain maximum / electric field maximum (Smax/Emax) was 330 pm/V. Transmission electron microscopy revealed ferroelectric-like domain structure in the 0.3BT-0.1BMT-0.6BF ceramics.