title: Unidirectional spaser in symmetry-broken plasmonic core-shell nanocavity.
abstract: The spaser, a quantum amplifier of surface plasmons by stimulated emission of radiation, is recognized as a coherent light source capable of confining optical fields at subwavelength scale. The control over the directionality of spasing has not been addressed so far, especially for a single-particle spasing nanocavity where optical feedback is solely provided by a plasmon resonance. In this work we numerically examine an asymmetric spaser - a resonant system comprising a dielectric core capped by a metal semishell. The proposed spaser emits unidirectionally along the axis of the semishell; this directionality depends neither on the incident polarization nor on the incident angle of the pump. The spasing efficiency of the semishell-capped resonator is one order of magnitude higher than that in the closed core-shell counterpart. Our calculations indicate that symmetry breaking can serve as a route to create unidirectional, highly intense, single-particle, coherent light sources at subwavelength scale.
authors: School of Electrical & Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907, USA. meng14@purdue.edu
authors: Xiangeng
authors: X
authors: Meng
authors: Urcan
authors: U
authors: Guler
authors: Alexander V
authors: AV
authors: Kildishev
authors: Koji
authors: K
authors: Fujita
authors: Katsuhisa
authors: K
authors: Tanaka
authors: Vladimir M
authors: VM
authors: Shalaev
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