Quasi-whispering gallery modes in ZnO microtowers

Abstract

We show that the laser spectra of ZnO films composed of particles that look like microtowers represent two bands with practically constant spectral distances between their peaks. By numerical analysis, we show that these two bands are due to whispering gallery modes (WGM), and one of these bands corresponds to the quasi-whispering gallery mode. Thus, we obtain here the first clear demonstration of the existence of quasi-WGMs, and show, in addition, that the width of the bands is caused by random spread of sizes of the ZnO particles in the lasing part.