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We demonstrate that the near field enhancement of sub-wavelength slits can be experimentally determined in the far field by using a reference aperture. Our simple model derived from the Kirchhoff integral formalism shows that enhancement of the near field at a slit exit with respect to the incident wave can be read in the transmitted amplitude through the slit attached on a reference aperture, normalized...
We report on the terahertz modulation based on the micro- and nano- sized apertures with metal-insulator phase transition of VO2 thin film. Terahertz wave transmission through subwavelength apertures is controlled by temperature driven refractive index change of VO2 substrate.
We measure field enhancement through nanogap by using both terahertz time domain spectroscopy (TDS) and terahertz imaging technique with continuous wave (CW) radiation source. Far-field amplitude is connected to the near-field enhancement through the Kirchhoff formalism. With TDS, we found that a field enhancement of 200 at 0.1 THz for the 500 nm slit. To confirm our TDS results, we also perform the...
We have measured transmission properties of a composite structure consisting of nano-rods on a long (ay = 300 micron) nano gap (70 nm) on Au film in broad frequency range of 0.1 THz to 1.0 THz using THz time-domain spectroscopy. The normalized transmittance with no nano-bridge or nano-rod structure in the middle shows a half-wavelength resonance: the resonance frequency is ~c/(2nay) where n is the...
We show that terahertz waves transmit through a lambda/30,000 nanogap separating two conducting planes. The field enhancement responsible for the light funneling has a 1/f dependence, which originates from the charging time of the gap.
By using terahertz (THz) time-domain spectroscopy we measured THz-electromagnetic pulse passing through a two-by -two subwavelength hole matrix in near-field regime. Our Fourier analysis of measured data shows detection position dependent transmission maxima with respect to the polarization direction of the incident field. By comparing with numerical simulations based on finite element method, we...
We present results on THz near-field measurements of sub-wavelength single holes made in metal. Time and frequency dependence of the electric near-field of single sub-wavelength apertures are compared with the near-field predictions made by the well-known Bethe-Bouwkamp model.
An array of sub-wavelength circular apertures (d=60 mum), periodically distributed in a square lattice, was studied in the near field using Terahertz Time-Domain Spectroscopy (THz-TDS). Images of the complete electric field distribution (Emacrx,Emacry,Emacrz) were recorded over a subsection of the array, as well as the corresponding spectral information, with a spatial resolution Lt10 mum.
We investigate surface wave generation by a single slit, both in nano-optical and in terahertz regimes. The wave-front in optical regime separates itself into forward propagating wave and surface-bound 90-degree diffracted wave; while, no such clear separation of modes is not observed in terahertz regime. Excitation wavelength dependency is systematically studied.
We performed time-domain terahertz spectroscopy on flexible films coated by single-walled carbon nanotube. The films demonstrate good shielding of electromagnetic waves in the terahertz range, maintaining good transparency for visible light. The shielding efficiency can be engineered by the thickness control of the film and by the chemical treatments.
We experimentally visualize Poynting vector of transmitted terahertz wave through a multiple slit array. This new method provides direct mapping of energy flow and helps distinguishing different diffraction orders in the near-field.
We report on the enhanced terahertz transmission at the fundamental shape resonance of the rectangular holes. The funneling of energy at the fundamental resonance is also confirmed at the near-field.
The transmission characteristic of a two-dimensional array of rectangular holes was examined theoretically and experimentally in the THz frequency range. The structure under consideration was found to act as a multi-frequency resonance filter whose frequency response of transmission depends on the periodicities and filling material of the structure.
Starting from terahertz time-domain spectroscopy, we obtain electric field vector images at each frequency component. We then synthesize images for diffraction from a single slit for an arbitrary incident waveform by inverse Fourier-transformation.
We investigate sub-wavelength diffraction by a single slit, both in nano-optical and in terahertz regimes. The wave-front in optical regime separates itself into forward propagating beam and surface-bound 90-degree diffracted wave, i.e., surface plasmon polaritons.
We experimentally study Poynting vector flows when terahertz waves transmit through a multiple slit arrays. Our methods provide a new way of visualizing energy flows and determining different diffraction orders in the near-field.
We present results on THz near-field measurements of sub-wavelength apertures in metal films. Our results allow us to test, with unprecedented detail, the near-field predictions made by the well-known Bethe-Bouwkamp model.
We report that the terahertz transparency occurs at the fundamental shape resonance of the rectangular holes regardless of the areal coverage. The funneling of energy at the fundamental resonance is also confirmed at the near-field.
We compare the near-field imaging of a free standing perforated metal film and a PMMA- graphite composite film with arrays of periodic holes at the terahertz frequency range of from 0.05 THz to 1.65 THz region.
A terahertz near-field imaging has been developed, spatiotemporally imaging both the amplitude and phase of the horizontal and vertical components of the electric field vector over the spectral range from 50 GHz to 1.5 THz.
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