Hexagonal Shaped ZnO Whispering Gallery Mode Microcavities
ABSTRACT :
ZnO hexagonal micro- and nanorods are regarded as important building blocks for nanoscale optoelectronic devices, because they provide high quality (Q) factors leading to strong optical feedback and sharp whisperings gallery modes (WGM) within the micro- and nanocavities [1]. Whispering gallery microcavities have potential applications in ultra small-mode-volume devices wherein the laser threshold comes down drastically and the reported lowest value of laser threshold is ~0.45 kW/cm2. The reduction in the laser threshold in WGM lasing is ten times lower in comparison to lasing in ZnO nanostructures. Liaoxin Sun et.al [2] reported on the direct observation of the strong exciton-photon coupling in a ZnO tapered whispering gallery.
High quality ZnO microrods on Si (100) substrate are prepared using nanoparticle assisted pulsed laser deposition (NAPLD) technique (Nd:YAG laser with λ = 355 nm operated at 10 Hz with a laser energy density of 2.7 J/cm2). It is found that the ZnO microrods have perfect hexagonal shape with various sizes, which allows the investigation of the cavity length dependence of WGM. We observed two sharp WGM modes from the Au coated ZnO microrods in the near bandedge region at room temperature. We have also synthesized MgZnO microrods, and observed deep UV WGM modes.