Thresholdless Nanoscale Coaxial Lasers
  The generation of coherent radiation in nanostructures has attracted considerable interest in recent years owing both to the quantum electrodynamical effects that emerge in small volumes, and to their potential for future applications. The progress towards exploring this size regime, however, has been hindered by the lack of a systematic approach to scaling down the mode as the structures shrink in size and by the high threshold power required for lasing in small cavities. Here we present a new family of metamaterial-like nano-cavities consisting of metallic coaxial nanostructures that solves both of these problems. The proposed nanoscale coaxial cavities can operate as thresholdless lasers, and their size is not restricted by the mode cut-off. Using these new nano-cavities we have succeeded to demonstrate for the first time thresholdless lasing in a broadband gain medium, and the smallest room temperature, continuous wave, telecom laser to date. The nanoscale coaxial cavities are the first systematic step towards unveiling the potentials of ultra small quantum electrodynamical objects in which atom-field interactions generate new functionalities. 
M. Khajavikhan, A. Simic, M. Katz, J. H. Lee, B. Slutsky, A. Mizrahi,   V. Lomakin, Y. Fainman
physics.optics