Optical whispering gallery mode (WGM) resonances have been observed in zinc oxide micro- and nanowire cavities. Using model calculations, the experimentally observed mode spectrum was reproduced. The effect has been observed for wire radii between 100 nm and 10 µm corresponding to angular mode numbers from 1 to about 250. The whispering gallery effect was used to determine the refractive index of the wires as a function of the photon energy and temperature. Under high excitation conditions, WGM lasing was observed. Two methods for calculating the complex resonant modes are presented: a simple plane wave model and the numerical solution of the Helmholtz equation for the given resonator geometry.
A typical photoluminescence (PL) spectrum showing WGM resonances and (inset) a scanning electron microscopy (SEM) image of a zinc oxide (ZnO) microwire.