The corner effect in hexagonal whispering gallery microresonators

Hexagonal microresonators were investigated regarding the influence of the nanometer scale geometry of their corners on light out-coupling, mode quality factor, and lasing threshold of whispering gallery modes (WGMs). For this purpose, ZnO microwires with hexagonal cross section grown by carbothermal vapor-phase transport were fabricated. It turned out that their corners can either be sharp (curvature radius r(C) < 10 nm) or be blunt (r(C) approximate to 400 nm). Blunt corners enhance light out-coupling of WGM in the low-excitation regime but otherwise increase mode linewidth. Sharp corners hinder light out-coupling at low excitations leading to long cavity photon lifetimes and facilitating room-temperature WGM lasing at lowest reported lasing thresholds of 73 kW/cm(2). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757572]