RESUMO
Transparent glass-ceramics (GCs) containing Co:Mg(Al,Ga)2O4 nanocrystals (mean diameter of 7-9 nm) are synthesized by heat treatments at 850-950°C from magnesium aluminosilicate glass nucleated by TiO2 and doped with Ga2O3 and CoO. The GCs exhibit a broadband A24(F4)âT14(F4) absorption due to the Co2+ ions, low saturation fluence (â¼0.5 J/cm2), fast recovery time of initial absorption (â¼300 ns), and high laser damage threshold (â¼20 J/cm2). They are used for passive Q-switching of a diode side-pumped Er,Yb:glass laser generating 3.1 mJ/20 ns pulses (peak power, 155 kW) at 1535 nm with a TEM00 output mode. The Q-switching performance of the Co:Mg(Al,Ga)2O4-based GCs is compared with that for various Co2+-doped GCs and Co:MgAl2O4 single crystal. The prepared GCs are promising for further applications in passively Q-switched Er:YAG and other Er crystalline (or ceramic) lasers.
RESUMO
We report on the development of novel saturable absorbers for erbium lasers based on transparent glass-ceramics (GCs) containing a mixture of cobalt-doped ß-willemite, Co2+:ß-Zn2SiO4, and zinc oxide, Co2+:ZnO, nanosized (10-14 nm) crystals. The structure of the parent glass and GCs is studied by x-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and Raman spectroscopy. Variations of absorption spectra with heat-treatment reveal that Co2+ ions from the parent glass enter the crystals of ZnO and ß-willemite. GCs are characterized by a broad absorption band due to the A24(F4)âT14(F4) transition of Co2+ ions in tetrahedral sites spanning up to â¼1.74 µm, relatively low saturation fluence, FS=0.75 J/cm2 at 1.54 µm, short recovery time, τ=830 ns, and high laser damage threshold, â¼14 J/cm2. By using the developed GCs in a diode-side-pumped Er, Yb:glass laser, 0.77 mJ/45 ns pulses are generated.
RESUMO
Detailed studies of the azimuthal dependence of the mean fragment and flow energies in the Au+Au and Xe+CsI systems are reported as a function of incident energy and centrality. Comparisons between data and model calculations show that the flow energy values along different azimuthal directions could be viewed as snapshots of the fireball expansion with different exposure times. For the same number of participating nucleons more transversally elongated participant shapes from the heavier system produce less collective transverse energy. Good agreement with Boltzmann-Uehling-Uhlenbeck calculations is obtained for a soft nuclear equation of state.
RESUMO
A new saturable absorber Q switch for 1.54-mum Er:glass lasers is presented. The saturable absorber is a transparent glass ceramic that contains magnesium-aluminum spinel nanocrystallites doped with tetrahedrally coordinated Co(2+) ions. We obtained Q-switched pulses of up to 5.5 mJ in energy and 80 ns in duration at 1.54 mum. The relaxation time of (4)A(2) ?(4)T(1)((4)F) transition bleaching was measured to be (450 ? 150) ns. Ground-state and excited-state absorption cross sections at 1.54-mum wavelength were estimated to be (3.2 ? 0.4) x 10(-19) cm(2) and (5.0 ? 0.6) x 10(-20) cm(2), respectively.