Lasing threshold dependence on excitation pulse duration in ZnO tetrapods

The dependence of the stimulated emission from ZnO tetrapods on the excitation pulse duration was studied. In all cases, clear lasing modes with a width of 0.5-0.8 nm were observed. However, lasing thresholds were significantly different. The thresholds observed were 57 μJ/cm2, 840 μJ/cm2, and 4.2 mJ/cm2for 250 fs, 120 ps, and 6 ns excitation pulses, respectively. The same trends (a decrease of lasing threshold with a decrease of pulse duration) are observed in samples with different tetrapod densities, although the differences become less pronounced in higher tetrapod density samples where lasing from multiple tetrapods can occur.