Fabrication of low-threshold ZnO nanorod array random laser using a laser-induced hydrothermal synthesis

Random lasers (RLs) have recently expected as unique speckle-free laser light sources for sensors and imaging. To improve the controllability of RLs, we had proposed a novel resonance-controlled RL, which were composed of agglomerated mono-dispersed spherical ZnO nanoparticles. Although the resonance-controlled RL showed unique features such as quasi-single-mode and low lasing threshold, it is difficult to realize efficient optical input-output and electrode formation using agglomerated nanoparticle film. In contrast, because a two-dimensional nanorod array can also induce light localization via in-plane multiple light scattering, the accessibility of excitation and lasing light in the vertical direction could be expected to be improved comparing with agglomerated nanoparticles. As the fabrication method of nanorod array structures, a laser-induced hydrothermal synthesis using a local heating by laser irradiation on a gold thin film has recently been proposed. Because, unlike the conventional hydrothermal synthesis method, this method can easily control the size of nanorods by the control of irradiated laser power and time, we attempted to realize the resonance-controlled two-dimensional RL in nanorod array structures. In the experiments, we succeed to induce random lasing in ZnO nanorod array structures fabricated by a laser-induced hydrothermal synthesis, and find that their thresholds and lasing probability strongly depend on the fabrication condition (irradiated laser intensity, growth time, precursor concentration). These results suggest the possibility to control the RL properties simply by tuning the irradiated laser conditions.