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Theophylline anhydrite single crystal thin enough for wide range THz transmittance spectroscopy could be grown by Temperature Difference Method in aqueous solution. Polarization dependent THz transmittance spectra of the crystal at 70 K were obtained by using a GaP CW THz spectrometer. Absorption lines existing at close frequency could be resolved each other successfully. Assignments of absorption...
The "Abbe barrier" may be completely broken by curvilinear (conical) 3D diffractive lenses with unique 3D super resolution (∼0.4λ0 and ∼0.8λ0 for transverse and axial respectively), but in contrast to the flat diffractive optic the curvilinear 3D diffractive conical optic allow to overcome 3D Abbe barrier with focal distance F more than F>2λ.
Intense terahertz pulses are used to investigate nonlinear carrier dynamics in Au thin films with different morphologies. From THz field-dependent transmission measurements, we found that the conductivity in percolated Au nanostructures increases with increasing the incident field strength. The measured complex dielectric dispersion was analyzed using the Drude-Smith model to discuss the dynamics...
We propose a novel THz material analysis approach which consists of a combination of a stratified dispersive model, an appropriate measurement configuration and a time-domain based fitting procedure. The measurement configuration is modeled as a stratified system where for each layer the light-matter interaction is realistically described. The method is illustrated for the industrial quality control...
In this paper, we present the particle-in-cell(PIC) simulation results of a novel Ka-band ring-shaped microstrip meander-line slow-wave structure(SWS). This study shows that, this miniature millimeter-wave power amplifier is capable of delivering an average output power greater than WOW within the bandwidth from 28 to 38 GHz, when the beam voltage and the beam current are 11411Vand 200mA, respectively.
A square helix slow wave structure is proposed for high gain millimeter wave TWTs. The electromagnetic characteristics of this structure are calculated by HFSS. It is shown that, compared with the equivalent circular helix with the same cross section perimeter, the square helix structure holds higher interaction impedance and lower normalized phase velocity, which indicates higher output power and...
An optical steerable terahertz zone plate is achieved utilizing the localized distribution of the transient electron plasma on a silicon wafer. Its focusing and imaging performances are experimentally demonstrated. The research prompts the development of steerable optical imaging elements.
The analysis of petrochemical samples by Terahertz (THz) spectroscopy is investigated. THz spectroscopy is a nondestructive, contact-free analysis method for the study of many different materials. In this work, we show that the THz spectra can be used to get different chemical and structural information from a potential hydrocarbon source. Density of the geological samples has the potential for valuable...
This work demonstrates THz wave amplification in a non-linear MgO:LiNbO3 crystal using a parametric process. The amplifier has gain in excess of 55dB. This system has potential applications in non-destructive sensing and imaging of a wide variety of materials.
Optimizing high-power ultrashort pulse amplifier using double-clad Yb-doped fiber, maximum output power of >3 W with a pulse width of 110 fs without pedestal component is obtained. Using this pulse, high-power high-efficiency broadband THz pulse generation is expected.
We report on all-fiber tunable terahertz (THz) signal generation based on a tunable Micro Electro-Mechanical System Vertical-Cavity Surface-Emitting Laser (MEMS-VCSEL) and a fixed wavelength VCSEL. The VCSELs pump a n-i-pn-i-p supperlattice broadband photomixer. Signals between 33 GHz and 690 GHz were successfully generated, with no fundamental limit towards larger tuning ranges.
Detection of explosives has always been an important fact for homeland security. Terahertz spectroscopy and imaging is an emerging, promising candidate in this field. We use time domain THz spectroscopy and we demonstrate that a methodology based on chemometrics is successful for discrimination of explosives and prediction of their concentration in complex samples made by mixture of products.
We demonstrated the conversion of thermal energy in the form of far- and mid-infrared using a micro rectenna, consisting of a spiral antenna coupled to an ultra-fast nanodiode, the so-called self-switching device (SSD). A maximum efficiency of 0.02 % was measured at a 973 K (700 °C) using a calibrated black-body radiator illuminating the rectenna. The relatively low efficiency was due to the impedance...
High quality Mn-Co-Ni-O (MCN) spinel films are prepared on Al2O3 substrate by RF magnetron sputtering (RF) and chemical solution deposition (CSD). The microstructural characterizations reveal the films present excellent crystallization and compact surface. The variable temperature electrical results show the films have temperature coefficient of resistance (TCR) of −3.8 %/K at 295 K. Based on the...
Topological insulators represent a new state of matter where bulk insulators exhibit metallic surfaces that are protected by time reversal symmetry. However, in common transport measurements residual bulk conductivity hinders the properties of the topologically protected surfaces. Alternatively, terahertz spectroscopy has recently been shown to be capable of discerning the bulk and surface carrier...
Time domain THz spectroscopy and 3D imaging are used for non-destructive analyses of modern pottery which was made using ancient and traditional technology. Our study demonstrates that the internal structure of this of Pre-Columbian civilizations Mochica type pottery can be revealed with the help of X-Ray images used as references.
Real-life applications of terahertz (THz) systems often require fast imaging of large field of view of opaque scenes. Such features have been demonstrated by the development of a complete reflection active THz imaging system that combines QCLs as sources and antenna & cavity coupled micro-bolometer as THz video camera. While better than 5 mm resolution images of 40×60 mm² illuminated surfaces...
A FET detector, fabricated in a standard CMOS technology and coupled to a bow-tie antenna is characterized in terms of spatial response by using a deconvolution method. An optical setup is used to produce a predictable impulse response. The resulting spatial response shows interaction with other structures present on the chip, while the measured shape is in agreement with the antenna effective area...
Bow-tie antenna coupled field-effect transistors have been implemented in 0.25 μm AlGaN/GaN process technology and have been mounted on an aplanatic hemispherical silicon substrate lens. By asymmetric coupling of 590-GHz radiation to the channel, the transistors are used as direct power detectors, achieving system noise-equivalent power values of 166 pW/√Hz at 590 GHz (referred to the total beam power)...
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