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    ABSTRACT: In the present work, thermal effects in high-power diode lasers are investigated by means of high resolution thermography. Thermal properties of the devices emitting in the 650 nm and 808 nm wavelength ranges are compared. The different versions of the heterostructure design are analyzed. The results show a lowering of active region temperature for diode lasers with asymmetric heterostructure scheme with reduced quantum well distance from the heterostructure surface (and the heat sink). Optimization of technological processes allowed for the improvement of the device performance, e.g. reduction of solder non-uniformities and local defect sites at the mirrors which was visualized by the thermography.
    Materials Science and Engineering: B. 09/2012; 177(15):1268–1272.
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    ABSTRACT: Fracture toughness, four-point bending strength of transparent spinel, Y2O3 and YAG ceramics in function of temperature (from room temperature up to 1500° C) were measured. Creep resistance at 1500–1550° C was studied too. Grain size distribution was determined on polished and etched surfaces of samples. Fracture surfaces after tests were examined by scanning electron microscopy. The obtained results showed that: in the case of spinel ceramics fracture toughness and strength decreased from 20 to 800° C, increased from 800 to 1200° C and decreased at higher temperature; in the case of Y2O3 ceramics they increased from 400 to 800° C, and next kept constant up to 1500° C; in the case of YAG ceramics they kept constant from 20 to 1200° C and then decreased. The creep strain rate was measured for spinel and YAG but not for Y2O3 ceramics which appeared creep resistant. The hypotheses concerning toughening and creep mechanisms were proposed.
    Ceramics International. 08/2012; 38(6):4517–4524.
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    ABSTRACT: The particle composites Al2O3/(2 and 3Y)TZP and MgAl2O4/3Y-TZP were tested in bending at temperature of 1280 °C over strain rates from 3.4 × 10−7 to 1 × 10−4 s−1 and over stresses from 23 to 85 MPa. Strain rate of the composites decreased as a volume fraction of Al2O3 or MgAl2O4 increased. MgAl2O4/3Y-TZP composites deformed easier under the comparable conditions than alumina/zirconia composites. Four models of composite creep behaviour were compared to the experimental data. All the models were unsuitable for MgAl2O4/3Y-TZP, in turn an isostress, an isostrain and a constrained isostrain models provide the good predictions for creep rates for alumina/zirconia ceramics, but the rheological model appeared not good. The threshold stresses approach seems to be useful for describing superplastic flow of MgAl2O4/3Y-TZP composites.
    Journal of the European Ceramic Society 01/2012; 32(1):1–8.

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