Yasuto Miyazawa

Homogeneous nucleation of crystalline gallium from liquid gallium

Abstract The nucleation rate of crystalline gallium from supercooled liquid gallium was measured using a dilatometric technique. The results appear to represent homogeneous nucleation. They may be explained by ‘classical’ nucleation theory upon assumption of a negative interfacial entropy of formation.

Stress-birefringence associated with facets of rare-earth garnets grown from the melt; A model and measurement of stress-birefringence observed in thin sections

Abstract A model where stress-birefringence associated with a facet is due to strain induced by lattice mismatch between the facet and the surrounding off-facet regions is proposed. In order to prove the validity of the model, the stress-birefringence associated with 〈211〉 facets of pure YAG grown by the Czochralski (CZ) method and pure NdGG grown by the floating zone (FZ) method was measured using two different methods: (1) using a “rectifier” polarizing microscope with a Brace-Kohler compensator and (2) Senarmonts method using a He-Ne laser. The results of the quantitative measurements supported the validity of the mode. The experimental result, moreover, that the stress-birefringence associated with a facet of YAG was decreased by Cr 2 O 3 doping also supported it.

STARK SPLITTING SCHEME AND AN INDUCED EMISSION CROSS SECTION OF TBALO3

Detailed absorption and emission spectra on TbAlO3 are measured at room temperature and liquid-nitrogen temperature. By decomposition of the spectra, the Stark splitting scheme is established for 7F6, 7F5, and 5D4 multiplets of Tb3+ ions in TbAlO3 together with the peak energies in the Fourier transform infrared spectrum at liquid-nitrogen temperature. The multiplets are split into their maximum number of levels, which shows that the point symmetry is low for the Tb3+ ion site in TbAlO3. An induced emission cross section is estimated using the results of decomposition at liquid-nitrogen temperature to be 3.55×10−19 cm2. This value is comparable to the cross sections reported for Nd:Y3Al5O12, which is a well known solid-state laser material. The population inversion threshold is also estimated for TbAlO3 in comparison with Nd:Y3Al5O12. It is found that the threshold value for TbAlO3 is only about three times larger than that for Nd:Y3Al5O12. This TbAlO3 may have the potential to be a laser material with a ...

Origin of difference in lattice spacings between on- and off-facet regions of rare-earth garnets grown from the melt

Abstract Stress-birefringence of CZ- and FZ-grown YAG, FZ-grown NdGG, FZ-grown SmGG and FZ-grown GGG was observed in sliced sections perpendicular to the growth axis, and the maximum stress-birefringence (Δ n max ) observed at the boundary between the facet and off-facet regions was measured using a Brace-Kohler compensator under a polarizing microscope. As a result, certain characteristics of the stress-birefringence associated with the facet were revealed as (1) similarity in various rare-earth garnets, (2) ineffectiveness of annealing and (3) ineffectiveness of atmosphere constituent. Because the maximum stress-birefringence is proportional to the difference in lattice spacings between the facet and off-facet regions, these characteristics reflect the related characteristics of the lattice difference between the regions. From these observations, the origin of the difference can be attributed in the non-stoichiometry of rare-earth garnets between the two regions.

Flow in oxide melts in a high magnetic field

Abstract Magnetic-field-applied Czochralski equipment for oxide growth was designed and constructed. Using this equipment, it was possible to apply three types of magnetic fields in oxide melts. The flow in an oxide melt such as LiNbO 3 and TiO 2 in a high magnetic field was observed. It was found that the flows in oxide melts were very different from those in a semiconductor melt.

Stimulated emission cross section of Cr-doped GdScGa garnet

The stimulated emission cross section is calculated on the basis of emission spectrum and spontaneous lifetime measurements. The maximum stimulated emission cross section is determined to be 0.69×10−20 cm2. A comparison is made between the calculated stimulated emission cross section and one which has been determined from laser oscillation experiments. Fair agreement between them is obtained within a 20% error at wavelengths from 770 to 810 nm.

Growth of gadolinium indium gallium garnet (GInGG) single crystal by the floating zone method

Abstract A new garnet Gd 3 In 2 Ga 3 0 12 (GInGG) was synthesized by the sintering method from Gd 2 0 3 , In 2 0 3 and Ga 2 0 3 . Single crystals of Gd 3 In 2 Ga 3 0 12 were grown by the floating zone method. The obtained crystals were colorless and transparent. Their lattice constants were measured to be 1.266 nm.

Growth of gadolinium lutetium gallium Garnet (GLGG) single crystals by Czochralski method

Single crystals of Gd3Lu2Ga3O12 (GLGG) were grown by the Czochralski method. The obtained crystals were colorless and transparent. Their lattice constants were measured to be 1.26 nm.

The growth of (TbxGd1 − x)AlO3 single crystals by the Czochralski method

(Tb x Gd 1-x )AlO 3 single crystals were grown by the Czochralski method. The crystals grown from Tb-rich melts under a reducing atmosphere were both twin and crack free. It is generally difficult to grow single crystals without cracks from Gd-rich melts. The optical properties of the crystals could be controlled by substituting Gd for Tb.

The growth of DyAlO3 single crystals by Czochralski method

Perovskite-type rare-eart aluminate and gallate crystals are suitable as substrates for high T c oxide superconductor film. We were able to grow dysprosium aluminate DyAlO 3 (DAO) single crystals by the Czocbralski method. The obtained crystals bad no cracks and no twin boundaries