Mode Control of Random Laser Action Assisted by Whispering-Gallery-Mode Resonance

Whispering-gallery-mode (WGM) resonance manipulated random laser action has been proposed. To illustrate our working principle, lasing characteristics of ZnO nanorods decorated with SiO2 nanospheres have been investigated. It is found that with the assistance of SiO2 nanospheres the emission spectrum exhibits a very narrow background signal with a few sharp lasing peaks and a very small full width at half-maximum of less than 0.3 um. The differential quantum efficiency (eta d) of random laser action can be greatly enhanced by up to 735%. More interestingly, the wavelength of laser action of ZnO nanorods can be controlled by the decoration of different-size nanospheres. The underlying origin is attributed to the fact that the decorated nanospheres not only enable the generation of WGM resonance and enhance the peak emission intensity but also can serve as scattering centers. Cathodoluminescence mapping images of nanorods decorated with nanospheres and theoretical calculation based on the spherical cavity were utilized to confirm our proposed mechanism. These intriguing features manifest the tunability of mode-controlled random laser action by WGM resonance of nanospheres. Our discovery shown here may open up a new approach for the creation of highly efficient optoelectronic devices.