Kiyoshi Shimamura

Growth and characterization of lanthanum gallium silicate La3Ga5SiO14 single crystals for piezoelectric applications

Abstract We have successfully grown a new piezoelectric La 3 Ga 5 SiO 14 (LGS) single crystal, with dimensions of 1 or 2 inch in diameter, using the Czochralski technique. Coloring of the grown crystals was discussed. The device properties of LGS resonators and filters were demonstrated. The LGS single crystal showed superior properties for piezoelectric applications.

Crystal growth and structural characterization of new piezoelectric material La3Ta0.5Ga5.5O14

New piezoelectric La3Ta0.5Ga5.5O14 bulk single crystals were grown using the Czochralski technique. The crystal structure (space group P321, a=8.228(2), c=5.124(2) A) has been refined using single-crystal X-ray diffraction data with a precision corresponding to an R index of 0.04. Ta atoms were found to be ordered in the octahedral site coordinated by six oxygen atoms.

Epitaxial Growth of GaN on (1 0 0) β-Ga2O3 Substrates by Metalorganic Vapor Phase Epitaxy

Epitaxial growth of nitride compounds by the metalorganic vapor phase epitaxy (MOVPE) technique is demonstrated for the first time on β-Ga2O3 single crystal substrates, which are near-UV transparent and n-type conductive. High-quality (0 0 0 1) GaN epi-layer with a narrow bandedge luminescence was obtained using a low temperature conductive buffer layer. InGaN multi-quantum well (MQW) structure was also successfully grown. The first blue light-emitting diode (LED) on β-Ga2O3 with vertical current injection is demonstrated.

Growth and optical properties of ErVO4 and LuVO4 single crystals

Abstract We have successfully grown erbium vanadate (ErVO 4 ) and lutetium vanadate (LuVO 4 ) single crystals by a modified Czochralski method in which a high temperature gradient was maintained at the interface during growth. Refractive indices of these crystals were measured. They indicated large birefringence, 0.227 (ErVO 4 ) and 0.218 (LuVO 4 ). Both crystals showed a high transmittance from the visible to infrared region. The crystals were expected to be a new attractive polarizer material.

Chirped-pulse amplification of ultraviolet femtosecond pulses by use of Ce 3+ :LiCaAlF 6 as a broadband, solid-state gain medium

Chirped-pulse amplification in the ultraviolet region is demonstrated by use of a broadband Ce(3+): LiCaAlF(6) laser medium. A modified bow-tie-style four-pass amplifier pumped by 100-mJ, 266-nm pulses from a Q -switched Nd:YAG laser has a gain factor of 370 and delivers 6-mJ, 290-nm pulses. After dispersion compensation, the output pulses can be compressed to 115 fs.

Synthesis and characterization of Sr3TaGa3Si2O14 single crystals

New piezoelectric Sr3TaGa3Si2O14 (STGS) single crystals were grown using the Czochralski technique. The crystal structure of STGS is isostructural to that of Ca3Ga2Ge4O14, which has the trigonal space group P321 and Z = 1. The lattice parameters were a = 8.293(2) and c = 5.078(2) A. The final R-factors were R = 0.047 and Rw = 0.046 for 1406 unique reflections. The distribution of each cation was found to be ordered in each site. Some piezoelectric properties of STGS are reported.

Band Structures of Perovskite-Like Fluorides for Vacuum-Ultraviolet-Transparent Lens Materials

In the semiconductor industry, perovskite-like fluorides that have wide band gaps are potential candidates for vacuum-ultraviolet-transparent lens materials in optical lithography steppers. KMgF3 and BaLiF3 single crystals have already been grown, but materials with wider band gaps are desired. To find compositions more effective than KMgF3 and BaLiF3, we performed local density approximation (LDA) based ab initio band calculations for perovskite-like fluorides ABF3, where A and B include an exhaustive list of alkali metals, alkaline-earth metals, and other selected elements. We found that LiBeF3, NaBeF3, KBeF3, and RbMgF3 may have wider indirect band gaps than KMgF3 does. We also found that SrLiF3 may have a wider direct band gap than BaLiF3 does.

Growth and characterization of gadolinium vanadate GdVO4 single crystals for laser applications

We have successfully grown Nd3+-doped gadolinium vanadate ( Nd:GdVO4) single crystals by a modified Czochralski method in which a high temperature gradient was maintained at the interface during growth. Step faceting occurred during crystal growth and the cause of the faceting is discussed in relation to the growth conditions. Laser diode (LD) pumped laser oscillations were demonstrated. The Nd:GdVO4 single crystal showed superior lasing properties to Nd:YVO4 and Nd:YAG single crystals.

Birefringent- and quasi phase-matching with BaMgF 4 for vacuum-UV/UV and mid-IR all solid-state lasers

BaMgF(4) is a ferroelectric fluoride which shows a very wide transparency range extending from 125 nm to 13 microm. The conjunction of these properties confers to BaMgF(4) a unique chance for optical applications in the UV and mid-IR wavelength regions, where other nonlinear materials cannot be used. In particular its application as frequency converter in all solid-state lasers is considered. The wavelength dispersion of the refractive indices along the three optical principal axes is measured in the transparent region, and the Sellmeier coefficients for the three refractive indices are determined. The conditions for nonlinear optical processes are calculated for birefringent-matching and quasi phase-matching, with special emphasis in the UV and IR wavelength regions. Quasi phase-matching can be achieved in the whole transparent wavelength region, in contrast to birefringent-matching, which can be obtained in a limited range 573-5634 nm. First demonstration of second harmonic generation by quasi phase-matching with a ferroelectric fluoride is shown by frequency-doubling the emissions of a 1064 nm Nd:YAG laser and a tunable Ti:sapphire laser. The shortest emission is obtained in the UV at 368 nm, indicating the potential of BaMgF(4) as nonlinear medium for the fabrication of all solid-state lasers in the vacuum-UV/UV and mid-IR wavelength regions.

Crystal growth of Ce-doped and undoped LiCaAlF6 by the Czochralski technique under CF4 atmosphere

Ce-doped and undoped LiCaAlF6 (LiCAF) single crystals 50 mm in diameter were grown by the Czochralski technique. The formation of inclusions and cracks accompanying the crystal growth was investigated. The dependence of lattice parameters on the temperature was measured for LiCAFand LiSrAlF 6 single crystals. Linear thermal expansion coefficients for both these crystals were evaluated. Higher transmission properties for LiCAFsingle crystals were achieved in the UV and VUV wavelength regions. # 2001 Elsevier Science B.V. All rights reserved.