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The stimulated emission spectra of ZnO powder as a function of the excitation area with a fixed peak pump intensity of .
CBC at . (a) Angular dependence of the backscattering peak for the probe beam only and fitted with the three-dimensioanl coherent backscattering equation to obtain a transport mean free path . (b) Enhancement and sharpening of the CBC when pumped with a beam above the random lasing threshold at zero time delay relative to the probe beam. The backscattering cone is considerably noisier in case (b) than in case (a) because of the additional fluctuations from the high intensity pump beam and the pump-induced PL.
Picosecond decay of the CBC from the probe beam at the backscattered angle . The inset shows the corresponding time-integrated emission spectrum, which clearly indicates single mode random laser emissions at , and the probe continuum spectrum nicely overlaps with the single mode emission
Normalized time-resolved single mode random laser spectra showing the relaxation dynamics of the laser emissions and the PL background. The inset shows the decay of the spontaneous emission at and the single mode laser peak at . The dotted line shows only the decay dynamics of the stimulated laser emission obtained by subtracting the slow spontaneous PL background from decay curve (a), which resulted in a single exponential decay with a decay time constant of .
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