Abstract-Coherent Terahertz Radiation from Multiple Electron Beams Excitation within a Plasmonic Crystal-like structure

• Yaxin Zhang
• , Yucong Zhou
• , Yin Gang
• , Guili Jiang
•  & Ziqiang Yang

http://www.nature.com/articles/srep41116

Coherent terahertz radiation from multiple electron beams excitation within a plasmonic crystal-like structure (a three-dimensional holes array) which is composed of multiple stacked layers with 3 × 3 subwavelength holes array has been proposed in this paper. It has been found that in the structure the electromagnetic fields in each hole can be coupled with one another to construct a composite mode with strong field intensity. Therefore, the multiple electron beams injection can excite and efficiently interact with such mode. Meanwhile, the coupling among the electron beams is taken place during the interaction so that a very strong coherent terahertz radiation with high electron conversion efficiency can be generated. Furthermore, due to the coupling, the starting current density of this mechanism is much lower than that of traditional electron beam-driven terahertz sources. This multi-beam radiation system may provide a favorable way to combine photonics structure with electronics excitation to generate middle, high power terahertz radiation.

Abstract-Electrically tunable graphene anti-dot array terahertz plasmonic crystals exhibiting multi-band resonances

Electrically tunable graphene anti-dot array terahertz plasmonic crystals exhibiting multi-band resonances Peter Q. Liu, Federico Valmorra, Curdin Maissen, and Jerome Faist  »View Author Affiliations

http://www.opticsinfobase.org/optica/abstract.cfm?uri=optica-2-2-135

Optica, Vol. 2, Issue 2, pp. 135-140 (2015)
http://dx.doi.org/10.1364/OPTICA.2.000135

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Graphene-based plasmonic structures feature large tunability, high spatial confinement, and potentially low loss, and are therefore an emerging technology for unconventional manipulation of light. In this paper, we demonstrate electrically tunable terahertz plasmonic crystals consisting of square-lattice graphene periodic anti-dot arrays on a SiO2/Sisubstrate. Transmission spectroscopy reveals multiple distinct resonances arising from excitations of graphene surface-plasmon–polariton (SPP) modes on different branches of the SPP dispersion curves inherent to the periodic structures. The resonance frequencies are readily tuned electrostatically with the Si back-gate and exhibit the dependency on the carrier density unique to SPP in graphene. Simulations show excellent agreement with the experiments and further illustrate the symmetry-based selection rule for the excited graphene SPP modes. Such graphene plasmonic crystals may lead to a broad range of applications including plasmonic waveguide and transformation optics. Exploiting higher-order graphene SPP modes is an effective way to further facilitate field localization and enhancement.

© 2015 Optical Society of America

Plasmonic crystal alters to match light-frequency source

http://www.nanowerk.com/news2/newsid=32978.php#ixzz2j8YrxesW

(Nanowerk News) Gems are known for the beauty of the light that passes through them. But it is the fixed atomic arrangements of these crystals that determine the light frequencies permitted passage.

Now a Sandia-led team has created a plasmonic, or plasma-containing, crystal that is tunable. The effect is achieved by adjusting a voltage applied to the plasma. Because the crystal then is agile in transmitting terahertz light at varying frequencies, it could increase the bandwidth of high-speed communication networks and generally enhance high-speed electronics.

Sandia National Laboratories researcher Greg Dyer aligns a plasma-containing crystal that is tunable by varying the voltage. The technology potentially could increase the bandwidth of high-speed communications networks.

"Our experiment is more than a curiosity precisely because our plasma resonances are widely tunable," says Sandia researcher Greg Dyer, co-primary investigator of a recently published online paper in Nature Photonics ("Induced transparency by coupling of Tamm and defect states in tunable terahertz plasmonic crystals"), expected in print in November. "Usually, electromagnetically induced transparencies in more widely known systems like atomic gases, photonic crystals and metamaterials require tuning a laser's frequencies to match a physical system. Here, we tune our system to match the radiation source. It's inverting the problem, in a sense."

Photonic crystals are artificially built to allow transmission of specific wavelengths. Metamaterials require micron- or nano-sized bumps to tailor interactions between manmade structures and light. The plasmonic crystal, with its ability to direct light like a photonic crystal, along with its sub-wavelength, metamaterial-like size, in effect hybridizes the two concepts. Its methods could be used to shrink the size of photonic crystals and to develop tunable metamaterials.

The crystal's electron plasma forms naturally at the interface of semiconductors with different band gaps. It sloshes between their atomically smooth boundaries that, properly aligned, form a crystal. Patterned metal electrodes allow its properties to be reconfigured, altering its light transmission range. In addition, defects intentionally mixed into the electron fluid allow light to be transmitted where the crystal is normally opaque.

However, this crystal won't be coveted for the beauty of its light. First, the crystal transmits in the terahertz spectrum, a frequency range invisible to the human eye. And scientists must tweak the crystal's two-dimensional electron gas to electronically vary its output frequencies, something casual crystal buyers probably won't be able to do.

Source: Sandia National Laboratories