Visible-light plasmonic nanolaser uses dark lattice modes

Aalto University researchers developed a visible-light plasmonic nanolaser that uses dark lattice modes.

Researchers at Aalto University are using dark lattice modes from silver nanoparticles to create a visible-light plasmonic nanolaser. (Image credit: Aalto University)
Researchers at Aalto University are using dark lattice modes from silver nanoparticles to create a visible-light plasmonic nanolaser. (Image credit: Aalto University)

IMAGE: Researchers at Aalto University are using dark lattice modes from silver nanoparticles to create a visible-light plasmonic nanolaser. (Image credit: Aalto University)

Researchers at Aalto University (Espoo, Finland) are the first to develop a plasmonic nanolaser that operates at visible light frequencies and uses so-called dark lattice modes.1 The lifetimes of light captured in nanolaser dimensions are so short that the light wave has time to wiggle up and down only a few tens or hundreds of times. The results open new prospects for on-chip coherent light sources, such as lasers, that are extremely small and ultrafast.

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The laser operation in this work is based on silver nanoparticles arranged in a periodic array. In contrast to conventional lasers, where the feedback of the lasing signal is provided by ordinary mirrors, this nanolaser uses radiative coupling between silver nanoparticles. These 100 nm sized particles act as tiny antennas. To produce high intensity laser light, the inter-particle distance was matched with the lasing wavelength so that all particles of the array radiate in unison. Organic fluorescent molecules were used to provide the input energy (the gain) that is needed for lasing (see video below):

A major challenge in achieving lasing this way was that light may not exist long enough in such small dimensions to be helpful. The researchers found a smart way around this potential problem: they produced lasing in dark modes.

"A dark mode can be intuitively understood by considering regular antennas: A single antenna, when driven by a current, radiates strongly, whereas two antennas -- if driven by opposite currents and positioned very close to each other -- radiate very little," explains professor Päivi Törmä. "A dark mode in a nanoparticle array induces similar opposite-phase currents in each nanoparticle, but now with visible light frequencies," she continues.

"Dark modes are attractive for applications where low power consumption is needed. But without any tricks, dark mode lasing would be quite useless because the light is essentially trapped at the nanoparticle array and cannot leave," adds staff scientist Tommi Hakala.

"But by utilizing the small size of the array, we found an escape route for the light. Towards the edges of the array, the nanoparticles start to behave more and more like regular antennas that radiate to the outer world," says Ph.D. student Heikki Rekola.

REFERENCE:

1. T. K. Hakala et al., “Lasing in dark and bright modes of a finite-sized plasmonic lattice,” Nature Communications; DOI:10.1038/NCOMMS13687.

SOURCE: Aalto University; http://www.aalto.fi/en/current/news/2017-01-03/

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