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A design of a G-band TE01 mode converter is presented in this work. It consists of a TE01 mode launcher followed by a tapered waveguide section. Full-wave simulated reflection coefficient of stainless steel converter is better than −15 dB and transmission coefficient is better than −1.5 dB in a frequency range from 173 GHz to 193 GHz. The design is useful in applications employing highly overmoded...
Using newly developed silicon micromachining technology that enables low-mass and highly integrated receivers, we are developing state-of-the-art terahertz spectrometer instruments for space-based planetary and astrophysics orbiter missions. Our flexible receiver with integrated antenna architecture provides a powerful instrument capability in a light-weight, low-power consuming compact package which...
In the THz spectral region quantum detectors are intrinsically limited by the small energy of the electronic transition involved in photon absorption. To overcome this problem and improve detector performances, we propose novel approaches in which concepts borrowed from high frequency electronics and metamaterials are exploited to realize THz detectors. In particular, we have investigated sub-wavelength...
Terahertz (THz) streaking at individual sharp metallic tips allows for the control of photoelectron pulses in nanoscale volumes. The time-varying acceleration in the enhanced THz near-field facilitates a reshaping of electron energy spectra, corresponding to a manipulation of the phase space distribution. Here, we discuss our recent experimental and theoretical work on THz near-field streaking, with...
We combine sub-cycle, mid-infrared spectroscopy and near-field microscopy to achieve a spatial resolution of 25 nm and a temporal resolution of 50 fs. Using our nano-FTIR technology we can spatially, temporally and spectrally resolve the femtosecond carrier-dynamics in solid state materials like photo excited InAs nanowires.
THz electron spin resonance (ESR) measurement has been a powerful means to study magnetic systems due to the advantages of high spectral resolution, ESR measurement beyond the zero field splitting or the magnetic phase transition. We have been developing this THz ESR system, and we are now extending our developments to the multi-extreme THz ESR. Here the multi-extreme includes the high magnetic field,...
In this report we demonstrate a high-spectral-resolution terahertz (THz) imaging system on the basis of a THz quantum-cascade laser (QCL), a fast scanning mirror (FSM), and a cryogenic-cooled Ge:Ga detector. During the scan through an absorption cell filled with methanol (CH3OH), spectral information is obtained through QCL frequency tuning within a range that covers the feature of interest. Our results...
We explore the nonlinear optical properties of plasmonic semiconductor antennas resonant in the mid infrared. The nanostructures are fabricated on silicon substrates from heavily doped germanium films with a plasma frequency of 30 THz, equivalent to a wavelength of 10 μm. Illumination with ultrashort pulses at 10.8 μm produces coherent emission at 3.6 μm via third-harmonic generation.
We report possible light-induced superconductivity in the organic molecular solid K3C60, a superconductor at equilibrium below Tc=20 K. In our experiment we excited this alkali-doped fulleride with strong femtosecond pulses, tuned to be resonant with local molecular vibrational modes. By means of THz time-domain spectroscopy, we detected the pump-induced changes in the conductivity spectrum as a function...
An active all-optical high-efficiency broadband terahertz device based on an organometal halide perovskite (CH3NH3PM3, MAPbI3)/inorganic (Si) structure is investigated. Spectrally broadband modulation of the THz transmission is obtained in the frequency range from 0.2 to 2.6 THz, and a modulation depth of nearly 100% can be achieved with a low-level photoexcitation power (∼0.4 W/cm2). Both THz transmission...
An unconventional technique for fabricating single-crystal silicon microstructures is employed as a means of achieving high-efficiency terahertz resonators. The resonators are arranged in a homogeneous array, which is designed to operate as an artificial magnetic conductor with potential for applications in compact terahertz antennas. Experimental validation confirms zero phase change of the electric...
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...
Asymmetric coupled quantum wells in the conduction band of germanium grown on silicon wafers have been investigated by THz pump-THz broadband probe picosecond spectroscopy. The optically-pumped laser gain coefficient is estimated.
We performed measurements of plasma density in a “point-like” discharge, which is generated in a nonuniform flow of a gas (argon) under the action of high-power terahertz gyrotron radiation with a frequency of 0.67 THz, a power of 40 kW, and a pulse duration of 20 μs. The nonuniform flow was produced by injecting the gas to the vacuum chamber through a small hole (0.14 mm in diameter) under a background...
In ultra-wideband non-destructive testing of large multilayered polymers, data collection and reduction can be achieved by applying compressed sensing techniques. In this work, using effective modelling of possible defects, such as air gaps between layers, we construct defect dictionaries and use them as support data for a signal similarity-based classifier, which will automatically extract the main...
We have developed a stable two-mode laser by using a quantum dot optical gain chip in an external cavity. In this study, we demonstrate continuous change of frequency separation of a two-mode laser by using a birefringent etalon filter. Since the polarization of the quantum dot optical gain chip is TE-dominant, the frequency separation of the two-mode laser is controlled by rotating the birefringent...
Two laser driven THz electron injectors have been designed to be used as the gun in THz accelerating structures: First, a broadband multilayer structure which is capable of accelerating the electrons from rest up to 1.5 MeV kinetic energy using 2 mJ single cycle of THz signal. The second design is a four cell normal conducting cavity which is actually a narrow-band component and needs about 300 THz...
Mechanically tunable Bragg filters at terahertz frequencies are designed, fabricated by a simple procedure, and characterized via THz time-domain spectroscopy. The Bragg reflectors are composed by stacking thin cyclo-olefin Zeonor polymer layers, which are separated by spacers made of a bi-adhesive tape. The defect cavity is void and its thickness is mechanically tuned by means of a translation stage...
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.
We measured different sub-fractions of an asphaltene sample with a THz-TDS system. The results demonstrate good correlation between the terahertz absorption coefficient and the polarity of different sub-fractions.
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