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April 20th 2019

Worldwide, scientists are working to create nanoscale light sources. These can be used in LEDs, lasers and optical information technology. Researchers from this programme place nanophotonic structures around light-emitting molecules to influence how fast, in which direction, how brightly, and with which polarisation they emit light. One example of a nanophotonic structure is a plasmonic nano - antenna.

Building blocks
A metal nanoparticle located immediately next to a quantum light source, will act as such an antenna. Just like a radio antenna improves the transmission of radio waves, these optical antennae make the emission of photons more efficient. The idea behind the nano-antenna is that the light-emitting molecule causes a collective movement of electrons in the metal. This 'plasmon' then easily emits photons as a result of which the antenna efficiently emits light.

Besides antennae there are many other structures that influence emission of light. For example, structures that guide light or trap light. All of these components together form an extensive set of building blocks. Researchers from this programme want to know how these building blocks can best be combined to make useful systems. 'Building' a light system in this manner is comparable to electronics, where simple summation rules determine how resistors, capacitors and coils can be combined into circuits with a rich variety of functions. In 2013, the researchers successfully managed to expose a new universal design rule for making the best quantum light source.

Design rule
The AMOLF researchers made a circuit of about 500 nanometres in size using three building blocks: a fluorophore as an elementary light source, a mirror and a nano - antenna. It is known how the mirror and antenna individually influence the emission of light. By moving the mirror relative to the antenna at distances smaller than one-thousandth of the thickness of a hair, the researchers could accurately measure how the mirror and antennae add up to determine the 'resistance' experienced by the source. Surprisingly the usual calculation rules for series and parallel circuits that apply in electronics do not work in the case of light.

The new design principle will contribute to more efficient solar cells and LEDs, but also to quantum information applications in which information will be stored, processed or transported as single photons.