Low-threshold whispering-gallery mode lasing in large-diameter ZnO microrods

The development of efficient miniature laser sources ensuring low lasing thresholds and high $Q$-factors is one of the relevant aims of modern physics and materials science concerning micro- and nano-objects. In this work, lasing in the near ultraviolet range in ZnO microrods fabricated by pyrolytic carbothermal synthesis has been studied. The possibility of low-threshold lasing on whispering gallery modes in free-standing microrods with diameters of about 10 $\mu$m and larger has been demonstrated. A high optical and structural quality of such microrods, as well as their directional growth, ensures low lasing thresholds (down to 10–20 kW/cm$^2$) and high $Q$-factors (above 3000). It has been hypothesized that exciton recombination is responsible for stimulated emission in the microrods under study.