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We demonstrate a low-profile, holographic imaging system at millimeter wavelengths based on a frequency-diverse metasurface aperture. From measurements of spatially diverse field patterns, diffraction-limited images of human-scale targets can be reconstructed at diffraction and bandwidth limits. The system is driven by a single microwave source swept over a band of frequencies (18–26.5 GHz) and switched...
In this article we introduce a new type of frequency diverse antenna based on a leaky waveguide. We have shown with simulated experiment that the antenna can achieve 2cm spatial resolution at K-band frequencies.
We demonstrate the applicability of shape memory alloys for creating THz plasmonic structures that can be reversibly reconfigured. This is accomplished by training nickel titanium alloy free-standing foils to have two bistable temperatures between which the physical structure can be switched thermally. Specifically, we show that the metal foil can be switched between a flat foil and one that has either...
Surface wave provides unique applications ranging from biological sensing, deep-subwavelength lasing to plasmonic circuits. Seeking new approaches for controlling surface wave is highly desired in future integrated photonic devices. Here, we develop a versatile platform based on metasurfaces for the launch and control of propagating surface wave in the terahertz frequency regime.
We demonstrate that a nanostructured terahertz (THz) photoconductive detector enables sampling of THz fields localized on micrometer scale. The nanostructure, consisting of an optical nanoantenna array and a distributed Bragg reflector, acts as a hybrid cavity, which traps optical gate pulses within an optically thin photoconductive layer of the THz detector. This allows us to detect highly confined...
A conventional bull's eye antenna has a great potential to terahertz technologies, while its narrow band nature limits its ability for multi-frequency applications. Here we proposed an split-joint bull's eye (SJBE) structure with optimized aperture, which can achieve multi-frequency transmission and high concentration.
We report on a thickness dependence of the terahertz (THz) bull's eye antenna that uses surface plasmon. For the optimization of the device structure and the strong THz field enhancement, we investigate the thickness dependence of substrate for optimization. We achieved a high THz transmission through a sub-wavelength aperture and observed that the main peak has a weak dependence but the side peaks...
A conventional binary zone plate for terahertz focusing is compared with a proposed new configuration in which two zone plates are stacked, showing an increased focusing efficiency. The field intensity in the focal spot is enhanced by employing a low-loss cyclo-olefin polymer instead of more conventional materials.
A new class of accelerator based terahertz user facilities is presented in this paper. The prototype facility operates two superradiant THz sources in parallel providing simultaneously single cycle and multicycle THz pulses with an unprecedented combination of high field and high repetition rate. The THz generation is based on superradiant enhancement of radiation generated by relativistic electron...
In this paper we report the first results of the optical components development and the overall optical design for a wideband receiver to simultaneously cover ALMA bands 2 and 3. Two types of feed horns and OMTs have been designed to couple to the ALMA telescope beam using a modified Fresnel lens. Both types of hardware have been manufactured and tested in a near field beam scanner. The measured beam...
Terahertz imaging solutions for industrial non-destructive testing applications receive an increasing attention. Besides the need for real-time acquisition and image processing, 3D feature localization and large field of views of several tenths to a few meters are in the focus of interest. For this purposes sparse line arrays of transmitters (Tx) and receivers (Rx) offer an optimal approach to reduce...
We report on an analytical method for investigating the signal contrast obtained in near-field scanning millimeter-wave microscopy using a metal slit probe. The probe has a slit-like aperture at the open end of a rectangular metal waveguide. In our method, the electromagnetic field around the slit aperture at the probe tip is calculated from Maxwell's equations in the Fourier (wavenumber) domain in...
In feedhorn design, the power coupling to the fundamental free-space LG00 mode, or Gaussicity, is a good proxy for high performance, particularly the sidelobe and cross-polar levels and the near-field behavior. Gaussicity can be maximized by ensuring that the first few horn modes reach the aperture with the appropriate phase and amplitude relationship. We present two feedhorn designs for which the...
We investigate carbon-based materials (graphite, graphite nanofibers and multi-walled carbon nanotubes) using terahertz time-domain spectroscopy (THz-TDS). The THz-TDS of carbon-based materials has been especially useful for understanding of many fundamental physical properties (e.g. the electronic structure and electron-phonon interactions, etc.) of all sp2 carbons, given that carbon-based materials...
A set-up for the irradiation of biological samples in the frequency range from 18 to 40 GHz has been developed and characterized in terms of electric field patterns and SAR values at the plane of the culture medium and beyond. Simulations and measurements of the radiated electric field have been performed at the frequency of 25.28 GHz to evaluate the homogeneity of irradiation. This paper compares...
We present transmission properties of sub-wavelength apertures (<λ/100) and discuss their applications in the collection-mode near-field probe for use with terahertz time domain spectroscopy (THz-TDS). In the deep sub-wavelength regime, the aperture transmission contains mostly evanescent field components. We have characterized the transmission properties experimentally in the THz range for 2,...
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