2 research outputs found
Colossal Absorption of Molecules Inside Single Terahertz Nanoantennas
Molecules have extremely small absorption
cross sections in the
terahertz range even under resonant conditions, which severely limit
their detectability, often requiring tens of milligrams. We demonstrate
that nanoantennas tailored for the terahertz range resolves the small
molecular cross section problem. The extremely asymmetric electromagnetic
environment inside the slot antenna, which finds the electric field
being enhanced by thousand times with the magnetic field changed little,
forces the molecular cross section to be enhanced by >10<sup>3</sup> accompanied by a colossal absorption coefficient of ∼170 000
cm<sup>–1</sup>. Tens of nanograms of small molecules such
as 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and lactose drop-cast
over an area of 10 mm<sup>2</sup>, with only tens of femtograms of
molecules inside the single nanoslot, can readily be detected. Our
work enables terahertz sensing of chemical and biological molecules
in ultrasmall quantities
Plasmon Enhanced Terahertz Emission from Single Layer Graphene
We show that surface plasmons, excited with femtosecond laser pulses on continuous or discontinuous gold substrates, strongly enhance the generation and emission of ultrashort, broadband terahertz pulses from single layer graphene. Without surface plasmon excitation, for graphene on glass, ‘<i>nonresonant laser-pulse-induced photon drag currents</i>’ appear to be responsible for the relatively weak emission of both <i>s</i>- and <i>p</i>-polarized terahertz pulses. For graphene on a discontinuous layer of gold, only the emission of the <i>p</i>-polarized terahertz electric field is enhanced, whereas the <i>s</i>-polarized component remains largely unaffected, suggesting the presence of an additional terahertz generation mechanism. We argue that in the latter case, ‘<i>surface-plasmon-enhanced optical rectification</i>’, made possible by the lack of inversion symmetry at the graphene on gold surface, is responsible for the strongly enhanced emission. The enhancement occurs because the electric field of surface plasmons is localized and enhanced where the graphene is located: at the surface of the metal. We believe that our results point the way to small, thin, and more efficient terahertz photonic devices