Hisashi Minemoto

Intracavity second‐harmonic generation using a deuterated organic ionic crystal

A large organic ionic crystal (10×28×15 mm3):4‐nitrophenol sodium(:Na) salt dihydrate (NPNa) crystal, which had good optical, mechanical, and thermal properties, was grown for the second‐harmonic generation (SHG) device. Its effective nonlinear constant was found to be 5.0 pm/V at 1064 nm. The Vickers hardness and thermal conductivity were about two times larger than those of molecular crystals. The SHG device made of DNPNa, in which the water of crystallization of NPNa was deuterated, was used for the intracavity SHG of a diode‐pumped cw Nd:YVO4 laser. High SHG power of 4.4 mW at 532 nm was obtained for the first time with an organic nonlinear material.

Crystal growth and the nonlinear optical properties of 4‐nitrophenol sodium salt dihydrate and its deuterated material

Large organic ionic crystals on the order of a few centimeters of 4‐nitrophenol sodium(:Na) salt dihydrate (NPNa) and DNPNa, in which the water of crystallization of NPNa was deuterated, were grown for second‐harmonic generation (SHG). The Vickers hardness and thermal conductivities of NPNa were about two times larger than those of conventional organic molecular crystals. The effective nonlinear optical constants of NPNa and DNPNa were estimated to be 5.0 and 5.5 pm/V, respectively. The optical loss coefficients, measured by spectrophotometry, of NPNa and DNPNa were 1.8 and 0.6 dB/cm at 1064 nm, respectively. The substitution of D2O for H2O in NPNa crystal is very effective in reducing the optical loss coefficient. High power of 4.4 mW green SH light was obtained using a 1.5‐mm‐thick DNPNa crystal as the intracavity SHG device of a diode‐pumped Nd:YVO4 laser.

Mixed rare‐earth iron garnet (TbY)IG for magnetic field sensors

Temperature dependence of sensitivity constants, corresponding to Verdet constant, of dodecahedrally substituted (TbxY1−x)IG crystals grown by a conventional flux method and liquid‐phase epitaxy method are studied. By measuring the variation of the sensitivity constant with temperature, it was found that crystals with X=0.19 show a minimum value of ±1% between 300 and 400 K. The temperature dependence of sensitivity constants on Tb concentration was explained by a simple theoretical calculation.

Small optical magnetic-field sensor that uses rare-earth iron garnet films based on the Faraday effect

Highly accurate optical magnetic-field probe sensors that use iron garnet films have been developed. New probe-type sensors were designed with a confocal optical system. A new garnet composition, Bi(0.98)Gd(0.92)La(0.03)Y(1.07)Fe(4.72)Ga(0.28)O(12), was found that shows high temperature stability for a sensitivity of less than 2.0% from -20 to +80 degrees C. The linearity error of the sensor output was within 1.0% for alternating magnetic fields from 0.3 to 42 mT. An optical current transformer that uses the proposed sensor has an ac linearity of 1.0% for input current up to nearly 300 A. The sensor realized high performance in actual use.

Magneto‐optical properties of (BiGdY)3Fe5O12 for optical magnetic field sensors

The temperature dependent sensitivity characteristic in the zeroth‐order diffraction beam from the multidomain materials of BiXGdYY3−(X+Y)Fe5O12 films grown by a conventional liquid‐phase‐epitaxial method are studied. By measuring the variation of the sensitivity with temperature, it was found that films with X=1.3 and Y=0.43 show the minimum value of ±0.5% between 253 and 353 K. The contribution of the Gd substitution on the improvement of the temperature dependence of the sensitivity was explained by a simple theoretical calculation.

Optical Fiber Current Sensors Using Garnet Crystal for Power Distribution Fields

We introduce applied examples (already put to practical use) of power distribution fields of optical fiber current sensors using iron garnet crystal that have high sensitivity, high linearity and stable temperature characteristics. We also describe two types of new optical fiber current sensors developed recently aimed at cost reduction and high performance.

Temperature-stabilized optical isolator for collimated light using (BiLuGd) 3 Fe 5 O 12 /(BiGd) 3 (FeGa) 5 O 12 composite film

We have fabricated optical isolators whose temperature dependence of the isolation ratio has a stability of <0.2 dB using (BiLuGd)(3)Fe(5)O(12)/(BiGd)(3)(FeGa)(5)0(12) composite film. It has been confirmed that the temperature-dependent forward loss of the isolators originates from the thermal fluctuation of the absorption peak in the films. We have also evaluated the degradation of the isolation ratio for collimated light depending on the incident angle of the collimated light, the incident position with respect to the optic axis, and the wavelength range needed for practical use.

Intracavity Second-Harmonic Generation and Influence of Optical Loss of Organic Nonlinear Optical Materials

We propose two different methods to estimate the optical loss of organic nonlinear optical (NLO) materials, which significantly reduces the efficiency of intracavity second-harmonic generation. One method is the estimation of the optical loss from the intracavity optical power at 1064 nm. The optical loss of the 4-nitrophenol sodium (:Na) salt dihydrate (NPNa) crystal was 1.3 dB/cm, and that of the DNPNa crystal, in which the water of crystallization of NPNa was deuterated, was 0.15 dB/cm. Another method is the estimation of the optical absorption loss from a liquid, the molecular structure of which has the same particular structural groups as those of the organic NLO materials. This latter method is very useful when new organic NLO materials are designed. The optical absorption losses at 1064 nm for the particular structural groups of the benzene ring were found to increase in the following order: -Cl<-NO2<-CH3=-OCH3<-OC2H5<-NH2.

Preparation of (Bi1/2K1/2)TiO3-Bi(Mg1/2Ti1/2)O3-BiFeO3 Ceramics Withnanodomain Structure and their Piezoelectric Properties

Lead-free (Bi0.5K0.5)TiO3)-Bi (Mg0.5Ti0.5)O3-BiFeO3 (BT-BMT-BF) ceramics were prepared by a conventional solidstate synthesis. Synchrotron x-ray diffraction studies indicated two compositional phase boundaries. An increased strain of 0.070% was obtained at 50 kV/cm, 1 Hz, 25 °C for one of the phase boundary compositions of 0.45BKT-0.1BMT-0.45BF with the temperature of the dielectric maximum of 331 °C.