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A novel terahertz photoconductive antenna that totally suppresses unwanted echoes is demonstrated. This is achieved with a buried metal plane placed below the surface antenna structure and active layer, realizing a sub-wavelength cavity.
We systematically studied the mid-20th century Italian oil panel painting “After Fishing” by Ausonino Tanda using x-ray transmission and terahertz time-domain transmission and reflection spectroscopic imaging (THz-TDSI).
We report on the reflection properties of calibration targets required for calibrating the radiometric performance of the Microwave Sounder instruments for the MetOp-SG satellites prior to launch. Both fixed temperature, 80 K, and variable temperature, 80–315 K, targets are required to perform this task. The specifications, the preliminary baseline design of the target structure and its measured reflectivity...
Broadband terahertz time domain spectroscopy (THz-TDS) and time resolved terahertz spectroscopy (TRTS) were performed on a 54 μm thick chalcogenide glass (As30Se30Te40) sample using a two-color laser induced air plasma THz system in transmission and reflection configurations, respectively. Two absorption modes were observed at 2–3 THz and 5–8 THz. The photo-induced conductivity can be well described...
We have applied the terahertz (THz) time-domain spectroscopy (TDS) to revealing the mechanism of the relativistic Doppler reflection of the THz light from a photo-induced plasma layer in a silicon wafer. The velocity of moving plasma layer is estimated by the reflected THz waveforms as a function of pump and probe delay time. We found that the interaction time of the moving plasma front and the reflected...
We propose a novel reference-acquisition method that provides precise phase alignment for terahertz imaging. The method significantly improves the accuracy of the extracted sample optical properties and greatly improves the experimental efficiency compared to traditional reference methods.
We have experimentally realized a broadband THz modulator in a total internal reflection geometry using SiO2/Si gated monolayer graphene. The modulation depth in our device is up to 83% over the range of 0.2–0.6 THz, and can be further improved by extending the size of our modulator and using multiple reflections.
A carrier-envelope phase (CEP) shifter for broadband terahertz (THz) pulses was demonstrated. The CEP, the phase of the carrier frequency with respect to the peak of the THz pulses, is a key element in light-matter interactions in high fields, especially when few-cycle pulses are used. The CEP shifter was constructed by suitably arranging several prism wave plates. By rotating the wave plates, we...
We investigate hydration of series of simple alcohol molecules using time-domain THz and FTIR spectrometers. We show that accurate measurements using the THz-TDS setup capable of 70 dB dynamic range in 30 s, can be combined well with traditional THz-FTIR measurements and that the spectra obtained by both setups are consistent with each other. Further, the difference absorption spectra between the...
Automotive coating plays an important role in car industry. They protect the car bodies from various aggressive weathering and mechanical deformations. Though many techniques have been developed for car coating, there is still a demand for non-destructive characterization of multilayer coatings. Therefore, research on new measurement methods is still ongoing. In this paper, we investigate thin coating...
This paper investigates the limit of detection of the spectral fingerprints of a material to be identified by terahertz spectroscopy, when the material is bare or concealed by clothes. After a theoretical study to determine the minimum observable peak amplitude versus the refractive index and the coefficient of absorption of the sample material, we discuss the case of detecting the absorption peaks...
Terahertz (THz) sideband generation on a near-infrared (NIR) carrier has been recently demonstrated using quantum cascade lasers (QCL), with potential applications in wavelength shifting and THz up-conversion. However, the NIR wavelength range and nonlinear efficiency were severely limited by absorption. Here we overcome this drawback through a novel reflection geometry, whilst preserving a large...
We describe the microstructuring of a silicon surface to act as a spatially tunable dielectric layer. As an example, we show FDTD simulations and fabrication results of it used as an antireflective layer optimized for the terahertz region.
In terahertz spectroscopy, multi-layered samples often need to be measured, for instance in a liquid flow cell, and this complicates the extraction of material parameters. We present a spectroscopic parameter extraction algorithm for multilayer samples that can also be used to extract the thickness of an unknown sample layer.
It is commonly believed that most of naturally occurring transparent materials have small positive refractive indices around 1 in the terahertz waveband. However, metamaterials have made a paradigm shift and achieve the design of man-made materials with both on-demand electromagnetic properties and unprecedented refractive indices. Here, inspired by the metamaterial concept, we report a transparent...
In this paper we show how the act of measuring skin in vivo using a standard terahertz reflection imaging system affects the terahertz response. We found that even 5 seconds occlusion by the imaging window caused subtle changes in the THz response. As the occlusion time increases, the skin's surface water content increases which causes the refractive index of the skin to increase. This in turn leads...
Terahertz (THz) imaging and tomography are modern imaging techniques permitting 2D and 3D inspection of objects over a broadband frequency range. The enormous quantity of information is then obtained. To be analyzed efficiently, an automated 3D data and image processing tool is needed. We present a complete data and image processing sequence to perform non-destructive inspection obtained from time...
A visualization method was proposed for displaying a 3D distribution of scattering sources in an object by analyzing the terahertz pulse echo with 2D scanning of the object. The method was successfully applied to terahertz pulse-echo measurements of a plastic plate, including three artificial defects: metal rod, air gap, and water-filled gap.
The terahertz (THz) passive body scanner is used for monitoring parsons carrying concealed weapons and contrabands at such places as airports and stations. It takes images of radiation from objects and gives the information on positions, sizes and shapes of the object. However, it has not been enough for inspecting various illegal goods such as explosives, guns, knives, drugs and narcotics. We propose...
We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. The artificial-dielectric medium is made up of a stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. The lens is capable of focusing a 2 cm diameter...
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