Lasing performance of a dye-doped laser by encapsulating orange fluorescent dye 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) with different concentrations in a highly ordered three-dimensional (3D) inverted-opal titania (TiO2) photonic crystal (PC) microcavity was studied. The lasing threshold and laser quality were improved by optimizing the concentration of the laser dye DCM. When the concentration of DCM is optimized to 10-4 mol/l, the photoluminescence (PL) efficiency of DCM is sufficient to achieve lasing emission and meanwhile no fluorescence quantum quenching occurs. Therefore, the emission spectrum was greatly narrowed and the threshold was significantly improved, which reached 0.8 mJ pulse-1 cm-2. Our findings are promising results toward the realization of fabricating a highly efficient low-threshold organic laser.
GaAs/AlAs distributed Bragg reflectors (DBRs) are widely used in the gain chips of 1 μm wave band semiconductor disk lasers (SDLs) as an end/folded cavity mirror. Because the generated redundant heat in the active region of a gain chip mainly dissipates through the DBR, thermal conductivities of DBRs are crucial for the output performance of SDLs. For the purpose of more reasonable semiconductor wafer design, to improve the thermal management of SDLs, accurate thermal conductivities of DBRs with various layer thicknesses are under considerable requirement. By the use of the equilibrium molecular dynamics (EMD) simulation and the Tersoff potential, thermal conductivities of GaAs/AlAs superlattices with different layer thickness are calculated, and computed results are compared with reported data to verify the validity of the EMD simulation. The computed thermal conductivities of GaAs/AlAs DBRs using the EMD method show significant reduction in contrast to the bulk value. Compared to EMD simulation, analytic methods result in smaller values of thermal conductivities and get close to the bulk value much more slowly with increasing layer thickness. In the layer thickness of interest (60-100 nm), the Matthiessen rule with α=1 for GaAs and α=0.5 for AlAs is a practicable tool for thermal conductivity estimation.
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