Optical whispering gallery modes in dodecagonal zinc oxide microcrystals

We have investigated optical modes in zinc oxide micropillars with dodecagonal cross section using polarization-resolved microphotoluminescence spectroscopy. Luminescence spectra of such pillars show series of resonance lines with characteristic line widths and spacings. The spectral positions of the observed lines can be explained assuming a circular two-dimensional dielectric resonator. Lowest radial mode numbers (n=1,2n=1,2) indicate optical whispering gallery modes.