Yoshio Fujino

New piezoelectric crystal: Synthetic fresnoite (Ba2Si2TiO8)

A fresnoite (Ba2Si2TiO8) single crystal was grown from the melt by the Czochralski method. Synthetic fresnoite has an electromechanical coupling factor in the thickness shear mode of k15=0.28, and a resonance‐frequency temperature coefficient in this mode of Tfr=−33 ppm/°C. Fresnoite is considered to be superior to Ba2Ge2TiO8 for various piezoelectric applications because of the absence of microtwins observed in Ba2Ge2TiO8.

Crystal growth and fundamental properties of LiNb1−yTayyO3

Abstract LiNb1−yTayyO3 (LNT) crystals were grown by the Czochralski method under various conditions. Macroscopic defects such as cracks, bubbles and cellular structures appeared in some growing crystals. Cracks and bubbles generated in growing crystals largely depended on the pulling axis and the pulling rate, respectively. Fundamental properties, such as lattice constants, density, temperature dependence of dielectric constants and thermal expansion behavior, of LNT grown crystals were studied.

Dependence of Second Harmonic Generation on Crystal Inhomogeneity

Effect of the nonuniformity of the natural birefringence in a nonlinear crystal on second harmonic generation (SHG) is theoretically and experimentally studied. The second harmonic power at the phase‐matching temperature, the second harmonic power vs temperature, and the temperature bandwidth are calculated in terms of the gradient of the natural birefringence and compared with those from the SHG experiment using a cw Nd:YAG laser and Ba2NaNb5O15 single crystal. It is found that the second harmonic peak power is much depressed by the nonuniformity of the natural birefringence in a crystal. The oscillations in the second harmonic power vs temperature curve become broad and the temperature bandwidth increases with decreasing crystal homogeneity. Satisfactory agreement was obtained between theory and experiment. By analytical calculation the dependence of SH power on crystal length l, is expressed in terms of the inhomogeneity length li, which is defined as a measure of the length beyond which SHG is limited...

Electrooptic and ferroelectric properties of lithium tantalate single crystals as a function of melt composition

Electrooptic, electric, ferroelectric and optical properties of lithium tantalate single crystals are investigated as a function of the melt composition for Li-Ta mole ratios ranging from 0.8 to 1.2. The Curie temperature depends on the melt composition, but the dependence is not linear. Specific resistivity increases as Li concentration in the melt increases. Homogeneity of the natural birefringence becomes higher with increasing Li concentration. Optical loss decreases in crystals grown from Li-rich melts. The crystals become much more resistant to optical damage after annealing in an oxygen atmosphere at about 1000°C.

Optical Damage in LiTaO3

Optically-induced refractive index inhomogeneities (optical damage) in LiTaO3 are studied in terms of the variations of light extinction. A simple relation between the laser-induced natural birefringence and light extinction is presented. The effects of the melt stoichiometry, the poling procedures and the oxygen-annealing on the optical damage in LiTaO3 are examined from the measurements of extinction ratios. Furthermore, the observation of the thermal decay of extinction ratio indicates that the thermal activation energy is 1.1~1.3 eV based on the diffusion theory of Amodei. By an improved technique and treatments a LiTaO3 crystal which is made resistant to optical damage by an Ar-ion laser (4880 A) with power density as high as 14 kW/cm2 is successfully obtained.

Phase-Matched Electro-Optic Light Modulator

A new type of light modulator, in which incident light polarization is converted to perpendicular polarization by electro-optic effect of r51, was studied, using an a-cut LiTaO3 with a Li/Ta1.2 composition. A spatially periodic electric field for phase-matching between two crossed polarizations is generated by a pair of interdigital electrodes. The electrode period is changed along the light path so that phase-match condition can be satisfied over a wide temperature range. Birefringence inhomogeneity along the light path was found to contribute to wider operation temperature ranges. An extinction ratio of above 30 dB and 73% conversion with an applied voltage of 180 V were obtained in the modulator. Measured temperature characteristics were almost coincident with calculated values.

LIGHT EXTINCTION OF LITHIUM TANTALATE IN LIGHT MODULATION

A theory for light extinction of LiTaO3 in terms of the nonuniformity of its natural birefringence is presented. The local gradient of the natural birefringence is obtained by observing the fringe pattern appearing on the crystal between crossed polarizers, and the extinction ratios are measured using a He–Ne laser. Agreement between the expected and the observed values is quite good, and simple technique for evaluating the crystal quality for light modulation is established.

Determination of the Distribution Coefficients of Li2O into LiNbO3 by Phase Matching Temperatures

The authors derive that the variation in the phase matching temperature for second harmonic generation (SHG) along the pull direction of lithium niobate (LiNbO3) crystal is proportional to the fraction solidified, and propose that the distribution coefficients of Li2O into LiNbO3 could be determined by measuring these relationships for crystals grown from the melts of various compositions without analyzing the composition of a crystal. It is found that the distribution coefficients estimated by this technique are in good agreement with the equilibrium distribution coefficients given in the equilibrium phase diagram by Lerner et al.

a-Axis growth of tungsten bronze-type compounds PbO · xNb2O5 (x = 2.7)

Abstract Single or “block-less” crystals of PbO · x Nb 2 H 5 ( x = 2.7) were pulled by α-axis growth, which has been proposed as an appropriate growth direction. The hypothetical explanation for the “block” appearance was proved experimentally.