In this paper, recent progress made towards the development of transparent Nd doped ceramic yttria is presented.
Using 99.99% pure raw materials and with improved material processing techniques, Nd doped ceramic yttria test
samples greater than 99% transmission at 2000nm wavelength and bandedge <250nm have been produced. The test
samples were >1" x 1" x 10mm in dimensions. Nd ions were successfully incorporated into undoped ceramic yttria
material through diffusion process.
High power solid state tunable lasers have played an important role in providing the technology necessary for active remote sensing and would be very useful for space exploration. Many recent studies on diode-pumped solid state lasers have focused on polycrystalline ceramic lasers. We present our initial results on the material, optical, and spectroscopic properties of a solid-state ceramic laser material using neodymium doped Yttria (Nd:Y2O3). Using a proprietary scalable production method, spherical non agglomerated and monodisperse ceramic powders of Nd:Y2O3 are made that can be used to fabricate polycrystalline ceramic material disks with sintered grain size in a suitable range. Initially, we produced translucent material with good emission properties. In further studies we have successfully prepared transparent Nd:Yttria ceramic material. Polycrystalline ceramic lasers have enormous potential commercial applications, which include remote sensing, chemical detection and space exploration research. Furthermore, the cost to produce ceramic laser materials is potentially much lower than that for single crystal materials because of the shorter time it takes to fabricate the material and also because of the possibility of mass production. The polycrystalline ceramic material that we have produced will be characterized for its suitability as a diode pumped solid state laser. Different laser designs will be discussed including end-pumping schemes and the thin-disk laser configuration.
New materials with improved mechanical properties and high optical transmission in the full 3-5 micron MWIR region wavelength are required. Commercially available polycrystalline transparent Yttria, with >100 micron average grain size, does not perform satisfactorily in demanding applications because of its modest strength. One way to improve strength is to develop an ultra-fine grained material with acceptable optical transmission properties. To realize fine grains it is necessary to use other phases to inhibit grain growth during fabrication. A promising processing method comprises: (a) synthesis of an extended metastable solid solution by plasma melting and quenching, and (b) consolidation of the metastable ceramic powder to form dense submicron-grained (<1 micron) composites. Two ceramic composites containing 20 and 50 vol% of second phase are evaluated in this study. Optical transmission, hardness, and indentation fracture toughness are measured and correlated with structure.
We have synthesized nanostructured rare-earth doped silicates by two different methods: combustion flame - chemical vapor condensation (CF-CVC) and sol-gel processing. Substantial rare-earth concentrations (~ 8 wt. %) were achieved with no signs of concentration quenching. We have observed unprecedented spectrally broad/flat fluorescence emissions at 1.55 μm from the Er3+-doped materials, which we attribute to their unique nanostructures developed during heat treatments. In depth results of a combined XRD/TEM study monitoring the evolution of the nanostructure will be presented. The role of processing conditions, chemistry, and particle size will also be discussed.
YBCO films, having critical current densities in excess of 10 to the 6th A/sq cm at 77 K and transition temperatures of about 89 K, successfully deposited on close lattice matched substrate materials at substrate temperature in the range from 720 to 740 C, are presented. The critical current densities are 10,000 A/sq cm at 70 K and the critical temperatures are 82 K for the films deposited on sapphire substrates. Successful deposition of c-axis oriented YBCO films with a transition temperature of 85 K was also achieved on silver substrates. Detailed analyses of the films were carried out by X-ray diffraction, EDS, SEM, resistivity measurements, critical current density measurements, and magnetization susceptibility measurements.
MOCVD and PE-MOCVD are versatile growth techniques which are capable of producing high quality YBCO superconducting films. The use of these methods to grow YBCO films with Tc in the range 88-90 K and Jc(77 K) repeatably in excess of 10 exp 6 A/sq cm is reported. This can be accomplished at substrate temperatures as low as 730 C, in the case of MOCVD, and 670 C for PE-MOCVD, through the use of N2O as the oxidant source gas. Growth at temperatures down to 570 C has been demonstrated but as the cost of Tc decreasing to 72 K. Still, these results are very promising for development of a low temperature process for the growth of YBCO which will be compatible with active device technologies.
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