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We present a systematic analysis of geometry-dependent parasitics for THz sub-harmonic Schottky mixer diodes. In particular, the diode RF power coupling bandwidth has been studied, showing a trade-off between the air-bridge finger length and finger separation for operating frequencies beyond 1 THz.
We report on terahertz emission from n-GaN films under steady state interband photoexcitation at low temperatures. The properties of the terahertz photoluminescence allow us to conclude that the emission occur under capture of nonequilibrium electrons to ionized donor centers.
We report on the analytical capacity analysis of terahertz wireless communications supporting 275–325 GHz frequency band. Our goal in this paper is to provide design guidelines for close proximity links with transmission capacity beyond 100 Gbit/s.
Density functional theory calculations of its crystal elucidated that the absorption peaks of perylene 3,4,9,10-tetracarboxylic dianhydride in the THz region are caused by the frequency shift and the peak splitting of the in-phase and out-of-phase vibrations of two molecules in a crystal unit cell. Crystal-packing interactions are found to enable IR-inactive vibration in isolated molecules to become...
In this work, a reflectarray operating at 1 THz is designed and implemented using metal-dielectric resonant patch elements. The dimensions of the single elements are optimized through simulation to achieve a wide range of the reflection phase change. Based on the relation between the phase change and the patch size, the terahertz reflectarray is built up to function as a reflector deflecting an incident...
Sample preparation of pharmaceuticals for THz spectroscopy has much importance, as the THz spectra are often highly sensitive to crystal and/or molecular structure changes. In this study, nondestructive sample preparations will be proposed and examined.
We fully interpolated frequency gaps between THz comb modes by tuning mode-locked frequencies in dual fiber lasers used for generation and detection of THz comb. The resulting gapless THz comb implies a possibility to enhance the spectral resolution in THz spectroscopy down to the linewidth of each comb mode.
Vibrational spectroscopic analysis of theophylline in a wet granulation process was performed. An anhydride was converted to a monohydrate during the granulation and a dehydration of monohydrate progressed during the drying process. A C-N stretching would be affected by an interaction between theophylline and a binder under a wet granulation process.
A new detection technique for sampling of terahertz pulses based on heterodyne modulation of an optical probe due to the sum (or difference) frequency mixing is proposed and experimentally demonstrated in the Cherenkov phase-matched scheme using a Si-prism coupled LiNbO3 crystal. In this technique, only the variations in intensity of the sampling optical pulse are measured and no polarization optics...
The present paper describes two kinds of techniques aiming at improving THz imaging for detecting rust under coated steel plates. First, it is revealed that a THz camera considerably shortens the THz-imaging time, but fringe patterns due to high coherence light source sometimes prevent image concatenation. Second, a program flowchart to quantitatively estimate the degradation level of rust is also...
We proposed and demonstrated active control of terahertz optical activity via chiral patterned photo-excitation in a semiconductor with a spatial light modulator. This technique provides a new route to terahertz polarization modulators.
Harmonic transponders used nowadays for tracking small insects impede and obstruct their movements due to their large size and weight. The paper presents millimetre wave band unbiased harmonic transponder. It comprises of separate transmit and receive microstrip patch antennas and unbiased Schottky diode doubler. The transponder is conformal, miniaturized and suitable for short range insect tracking.
High-speed algorithm of THz-image processing was investigated for the tablets containing the chemical constituents of drugs. A THz time-domain spectroscopic image could be obtained by mechanical scanning of the sample stage and time waveforms per pixel were saved. A couple of data processing methods were applied in order to visualize the ingredients in the tablets. By the autocorrelation processing,...
We present a liquid crystal mixture with record birefringence at THz frequencies. The mixture is characterized using a standard THz-TDS system. The birefringence exceeds 0.35. Since the mixture simultaneously shows low absorption it is ideally suited for device applications.
Broadband circular antenna array with convolution constrains is addressed in this paper. The circular array processor is able to scan a beam azimuthally through 3600 with little change in either the beamwidth or the sidelobe level. The simulation result shows that the proposed processor steer the main beam at any arbitrary direction without using presteering delays and it has capability to cancel...
In this paper we present a switchable THz device based on a polymer stabilized liquid crystal. The influence on the THz properties of this bicontinuous liquid crystal polymer network system is investigated. The stabilization allows the use of only one pair of electrodes for switching.
We measured the absorption coefficient and the non-radiative lifetime of intersubband transitions in Germanium quantum wells by steady-state and pump-probe terahertz spectroscopy.
We report experimental evidence of intrinsic linewidth values approaching the quantum limit in far-infrared quantum cascade lasers through the measurement of their frequency-noise power spectral density and a thorough investigation of the physics behind it.
We evaluated performance of zero-bias, square-law GaAsSb/InAlAs/InGaAs tunnel diodes at frequencies up to 220 GHz. The detectors with submicron cross-sectional area demonstrated sensitivities above 500 V/W, and curvature coefficients of 20 V−1.
In this paper, Smith-Purcell effect, which utilizes metallic grating and electron bunches, was investigated for a new device of terahertz (THz)-wave generation. Femtosecond electron bunches induced multimode THz-wave at a frequency of <0.7 THz.
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