Nanopyramids beam light up and down

Nanopyramids beam light up and down

In this paper we design and experimentally demonstrate a new type of metallic nanoantenna array that can preferentially beam different colors of light up or down.  This nanoantenna array could solve a long-standing problem in LEDs, where the backwards emitted light is lost thereby limiting the efficiency of the device.  Our design principle is inspired by the 1983 theoretical work of Kerker et al., who predicted that particles with magnetic and electric response of equal strength can anomalously scatter more light backward or forward. Such effects are difficult to realize at visible frequencies since most materials respond very weakly to the magnetic field of light.  However, the advent of metamaterials – artificial structures possessing properties absent in natural materials – has given us the tools and the framework to design artificial magnetism in response to an applied electric field. The emergence of magnetism in this way is at the heart of magnetoelectric structures, such as the ones we explore.  In particular, the nanoantennas in our array have the shape of a pyramid, whose tapering and height enhance the magnetoelectric behavior. In addition, by making an array of  these pyramid-shaped nanoantennas we demonstrate collective effects, which in combination with the single-pyramid effects, yield an unprecedented mechanism to beam some colors of light up and others down.

 

 

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