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Journal of Applied Physics

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Zinc oxide -- Optical properties, Lasers -- Stability, Optical pumping, Metallic oxides, Electron microscopy, Nanoparticles


We report experimental results on the structural stability of optically pumped zinc oxide random lasers. We find that the lasing threshold is not entirely stable and depends on the accumulated light exposure received in pulsed optical pumping. We show that exposure levels below ∼1.5 kJ/cm2 improve the lasing efficiency and lower the lasing threshold. Beyond that value, however, lasing efficiency and threshold begin to degrade. Electron microscopy shows that the degradation is accompanied by morphological changes characteristic of melting. These changes become visible at an exposure of ∼0.7 kJ/cm2. We suggest that the melting is initially localized within nanometer areas and that the initial improvement is due to defect annealing. For exposures larger than 1.5 kJ/cm2, the melting zones connect, leading to deterioration. The findings apply to coherent and incoherent lasing. If stable output from ZnO random lasers is desired, lower lasing thresholds or higher damage thresholds are needed.


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