Osamu Kamada

Theoretical concentration and attainable temperature in solar furnaces

Abstract By taking the brightness distribution of the solar disc into consideration, the characteristics of solar furnaces provided with a paraboloidal concentrator were theoretically treated. The energy-concentration ratio, the concentration efficiency and the attainable temperature for a flat, a cylindrical, and a spherical target were calculated for the furnaces with different aperture ratio, the results of which were compared with the results obtained by assuming that there was a uniform brightness distribution of the solar disc.

Construction of a large solar furnace

Abstract This paper describes the construction of a large solar furnace of the heliostat type. A paraboloidal mirror, 10 meters in aperture and 3.1 in aperture ratio, is a mosaic composed of 181 segments that have been ground and polished accurately into portions of a paraboloid and aluminized by vacuum evaporation to form front-surface mirrors. A heliostat has a steel skeleton frame that can rotate on a circular track to change the azimuth. Seven mirror bands, each with 34 front-surface mirrors, are mounted on the frame and move synchronously to change the elevation. Following the sun image is done by both a time system and a servo-system. Some performance test results are also presented.

Magneto-Optical Properties of Cerium-Substituted Yttrium Iron Garnet Single Crystals Grown by Traveling Solvent Floating Zone Method

A cerium-substituted yttrium iron garnet (Y3-xCexFe5O12) single crystal was grown by the traveling solvent floating zone (TSFZ) method in an oxygen environment. Using a Fe- and Ce-rich solvent, high quality single crystals with smooth and lustrous surface were grown at a rate of 1.0 mm/h. The segregation coefficient of Ce was calculated approximately as 0.2 from the compositional profile in the grown crystals measured by electron probe X-ray microanalyzer (EPMA). The optical absorption coefficient and the Faraday rotation angle of Y2.82Ce0.18Fe5O12 at 1550 nm wavelength were 0.12 cm-1 and -740 deg/cm, respectively. The figure of merit of a Faraday rotator was 1423 deg/dB. The absorption loss and sensitivity of the same Y2.82Ce0.18Fe5O12 (d=0.6 mm) for the magnetic field sensor were 0.03 dB and 0.1%/Oe, respectively, at 1550 nm wavelength. These results suggest that cerium-substituted yttrium iron garnet is a high performance material for the Faraday rotator at 1550 nm wavelength.

Electro-Optical Effect of Bi4Ge3O12 Crystals for Optical Voltage Sensors

The electro-optical coefficient r41 of Bi4Ge3O12, corresponding to the sensitivity of the optical voltage sensor, and the temperature dependence of response characteristics to applied step voltage are studied. From these measurements, two kinds of dc drift are found to exist in Bi4Ge3O12 crystals. One is found to be due to the relaxation of the piezoelectric polarization (type (a)), and the other is explained as the deduction phenomenon by the thermally induced space-charge field (type (b)). By correcting for dc drift of type (a), the accurate value of r41=1.09?10-12 m/V is obtained at 855 nm wavelength.

Magnetic field sensors using Ce:YIG single crystals as a Faraday element

Magnetic field sensors based on creation of the Faraday effect by rotation magnetization in Ce:YIG crystals are studied. The large linear magnetic birefringence (LMB) of /spl Delta/n=-1.7/spl times/10/sup -4/ was observed in the Ce/sub 0.18/Y/sub 2.82/Fe/sub 5/O/sub 12/ crystal and it was found from both the calculation and experimental investigations that the LMB affects the linearity of the sensor output. The validity of the method of utilizing a pair of Ce:YIG crystals with an azimuthal angle of 90 deg in the optical axis is demonstrated as a method of improving these phenomena.

RING INTERFEROMETRIC VOLTAGE SENSOR USING LINBO3 CRYSTAL

In this work, optical voltage sensors based on ring interferometry are studied to enable the measurement of the DC voltage by introducing a phase modulation technique. From experiments using z-cut LiNbO3 crystals as linear electrooptic elements for the sensing element and the phase modulator, a high sensitivity of 1.5%/V and relative error within ±1% were obtained for DC voltage up to 200 V. It was also clarified that these characteristics satisfy the JEC1201-1PS standard accuracy.

A High Temperature X-Ray Diffractometer Using a Solar Furnace

Using a solar furnace, 10 m in aperture and 3.2 m in focal length, a high temperature X-ray diffractometer is constructed. By this apparatus, the thermal expansion of CaO was measured up to 2150°C.

Magnetic field optical sensors using (TbY) IG crystals with stripe magnetic domain structure

In this paper, a new type of magnetic field optical sensor based on Faraday effect created by the magnetization rotation process in each stripe magnetic domain is proposed. For these sensors, (Tb/sub 0.19/Y/sub 0.81/)/sub 3/Fe/sub 5/O/sub 12/ ((TbY)IG) crystals were used as Faraday element. At the wavelength of 1.3 /spl mu/m, the obtained sensitivity is 4.7/spl times/10/sup -3/ %/A/m. The small linearity error of the sensor output is also obtained in a wide dynamic range between 1 A/m and 10/sup 4/ A/m. When the magnetic field is applied perpendicularly to the easy axis, we consider that a linear magnetization curve without hysterisis is obtained by a rotation of domain magnetization. This assumption is confirmed by experiment. The experimental results such as the sensitivity, the linearity error and the signal-to-noise ratio were explained well by the proposed model.

Study of Optical Magnetic Field Sensor Using Cerium-Substituted Yttrium Iron Garnet Single Crystal

The linear magnetic birefringence (LMB) in Ce-substituted Y3Fe5O12 crystals grown by the floating zone method and its influence on the characteristics of optical magnetic field sensors were studied. It was found that the measured LMB values of Δn001=-1.2×10-4 and Δn111=-1.7×10-4 in the Ce0.17Y2.83Fe5O12 sample were three times as large as those in YIG. The influence of LMB on the linearity of the magnetic field sensor, which was based on the Faraday effect created by magnetization rotation, was estimated quantitatively from the analytical result obtained by the Jones matrix calculation method. It was found from both calculation and experimental investigations that LMB strongly affects the linearity of the sensor output. It was successfully demonstrated that use of a pair of Ce:YIG crystals was very effective in improving the sensitivity of the sensor output.

Photorefractive Effect in Bi4Ge3O12

The photorefractive effect in Bi 4 Ge 3 O 12 and its incident laser power and temperature dependence are studied. From these measurements, a very small photoinduced refractive index change, Δn=1.2×10 -6 (E a =2.5 kV/cm, I=97 mW/cm 2 ), is observed. The response times (the rise time and the decay time) show the sublinear intensity dependence as well as the photocurrent. The rise time and the decay time under illumination are in the range of 10-100 s. The decay time data are analyzed as double exponential curves, suggesting two types of charge-carrier dynamics contributions to the photorefractive effect