Colloidal-quantum-dot spasers and plasmonic amplifiers
  Colloidal quantum dots are robust, efficient, and tunable emitters now used in lighting, displays, and lasers. Consequently, when the spaser, a laser-like source of surface plasmons, was first proposed, quantum dots were specified as the ideal plasmonic gain medium. Subsequent spaser designs, however, have required a single material to simultaneously provide gain and define the plasmonic cavity, an approach ill-suited to quantum dots and other colloidal nanomaterials. Here we develop a more open architecture that decouples the gain medium from the cavity, leading to a versatile class of quantum-dot-based spasers that allow controlled generation, extraction, and manipulation of plasmons. We first create high-quality-factor, aberration-corrected, Ag plasmonic cavities. We then incorporate quantum dots via electrohydrodynamic printing18,19 or drop-casting. Photoexcitation under ambient conditions generates monochromatic plasmons above threshold. This signal is extracted, directed through an integrated amplifier, and focused at a nearby nanoscale tip, generating intense electromagnetic fields. This spaser platform, deployable at different wavelengths, size scales, and geometries, can enable more complex on-chip plasmonic devices. 
Stephan J.P. Kress, Jian Cui, Patrik Rohner, David K. Kim, Felipe V.   Antolinez, Karl-Augustin Zaininger, Sriharsha V. Jaya...
physics.optics cond-mat.mes-hall cond-mat.mtrl-sci physics.chem-ph