Shape-controlled crystal growth of Sr3NbGa3Si2O14 and Sr3TaGa3Si2O14 piezoelectric single crystal by micro-pulling-down method
We have grown the shape-controlled Sr<inf>3</inf>NbGa<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> (SNGS) and Sr<inf>3</inf>TaGa<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> (STGS) langasite-type crystals by the μ-PD method. Columnar-shaped SNGS and STGS crystals were grown using the Pt-Rh crucible with a columnar die in 3 mm diameter. Grown crystals indicated high transparency and approximately 3 mm diameter. Chemical phases of grown crystals were identified as a single phase of langasite-type structure. The lattice parameters of grown crystals were almost consistent with those of crystals grown by Czochralski (Cz) method. In the X-ray rocking curve measurements, the grown crystals indicated equivalent crystallinity to the crystal grown by Cz method.
Ce Concentration Dependence of Optical and Scintillation Properties for Ce Doped  ${\rm LiYF}_{4}$ Single Crystals
We have investigated effects of Ce concentration on optical and scintillation properties for Ce doped LiYF<sub>4</sub> [Ce:LiYF<sub>4</sub>] single crystals. Li(Y<sub>1-x</sub>,Ce<sub>x</sub>)F<sub>4</sub> single crystals with more than 75 % transparency were grown by micro-pulling-down method in the range of 0 ≤ x ≤ 0.03 and the crystals with x = 0.05, 0.1 had milky parts originated from remained starting materials. Photoluminescence spectra of all Ce:LiYF<sub>4</sub> crystals indicated two emission peaks from Ce<sup>3+</sup> ion which was substituted for Y<sup>3+</sup> ion site. Light yield and decay time of α-ray irradiation for Ce:LiYF<sub>4</sub> crystals were largely affected by Ce concentration and the largest light yield was observed for the crystal with x = 0.02. In contrast, the decay time systematically became faster with an increase of Ce concentration.
Integrated two-beam antenna array featuring dual-circular polarization
A concept of an integrated antenna array featuring two independent beams and dual circular polarization has been described. The antenna array consists of two radiating elements which are excited at two orthogonally placed feeding ports with the use of four appropriately connected 3-dB/90° directional couplers. Therefore, such an array generates two symmetrically located beams having right-handed circular polarization (RHCP) and identical two beams having left-handed circular polarization (LHCP). The presented concept has been verified by the design and measurements of an antenna array operating at 2.4 GHz frequency range.