Keiji Sumiya

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.

MAGNETIZATION OF CERAMIC Y-BA-CU-O AND BI-SR-CA-CU-O AFTER NEUTRON IRRADIATION

Magnetization of ceramic Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O superconductors was studied after neutron irradiation in the fluence from 2.4×1021/m2 to 1.8×1022/m2 at 60°C. The area of hysteresis loops was enhanced at low neutron fluence, followed by saturation and then a decrease at high fluence. In Bi-Sr-Ca-Cu-O, the degree of enhancement was smaller than in Y-Ba-Cu-O and the enhancement reached saturation at lower neutron fluence.

Variation of Composition in a Bi(Pb)-Sr-Ca-Cu-O Grain and the Influence of Mg and Ba Doping on Its Superconductivity

The 110 K phase (2223) and (Sr, Ca)-Cu-O phase exist in the Bi(Pb)-Sr-Ca-Cu-O ceramics. The Cu content varies in the perpendicular direction of platelike 2223 grains, but little variation is observed on the planer surface of the grains along their length. Only the 110 K phase was found in the X-ray diffraction pattern of Bi(Pb)-Sr(Ba, Mg)-Ca-Cu-O. Its electrical resistivity became zero at 110 K. By the partial substitution of Mg and Ba for Sr, the range of sintering temperatures in which we obtained a higher Tczero was much larger than that for Bi(Pb)-Sr-Ca-Cu-O.

UV SHG emission by the QPM technique using ferroelectric fluorides

Ferroelectric fluorides are the key materials for the SHG in the UV/VUV by the QPM technique. Ferroelectric characteristics and large single crystal growth are addressed. UV SHG emission is demonstrated with BaMgF4 QPM devices.

Material system for high performance DRAM-CSP

The /spl mu/BGA/sup (R)/ which Tessera Inc. developed is one of the most suitable chip scale packages (CSP) for high speed DRAMs. However, the larger the chip size, the harder it is to achieve high levels of package reliability. Based on the thermal stress analysis, we have determined the threshold values of elastic modulus and coefficient of thermal expansion (CTE) of both the adhesive film and the liquid encapsulant to achieve higher thermal cyclic properties. Through this study, we have developed new polymer alloys composed of a low modulus polymer and an epoxy resin. CSPs fabricated with the newly developed materials showed high reliability including thermal cyclic properties and solder reflow resistance at high temperature under Pb-free requirements.

Formation of 2223 Phase and Variation in Composition of Bi(Pb)-Sr-Ca-Cu-O Superconductors

Sintering of Bi1.6Pb0.4Sr2Ca2Cu3.6Ox for long time resulted in an increase of the volume fraction of the 2223 phase to 53%. The 2223 phase appears to take the form of flaky grains. The chemical composition of the constituents of the flaky grains are not exact stoichiometric proportions. Substances in the calcined powder start to react around 832°C, then change to (Sr,Ca)-Cu-O and an unknown phase at 862°C. Growth of the 2223 phase is enhanced between these two temperatures.

Superconducting Properties of Y-Ba-Cu-O Sheet by a Tape Casting Method

YBa2CuO3O7-δ (YBCO) superconducting sheets were successfully fabricated by a tape casting method. Critical temperature (Tczero) was 92.IK with a tape sintered at 940°C for 10 hours in oxygen. The (001) planes of YBCO particles were oriented parallel to the casting plane of the 9 green sheet. The highest Jc was 1,510A/cm2 at 77K in zero magnetic field. It is supposed that the grain orientation contributed principally to the enhancement of Jc of the YBCO sheet.