We have demonstrated and developed a W-band 30 W continuous-wave folded waveguide traveling wave tube (CW FWTWT) with 13.5-kV operation voltage and 4.8 dB gain flatness. In this paper, we quantitatively study the relationship between operating voltage and the key geometric dimensions of a folded waveguide, which is the key to the design of the low-voltage TWT. In addition, problems of improving beam

MEMS-based phase shifters show the best performance in terms of figure of merit, but their footprints are usually large and it is difficult to achieve several bits. This paper demonstrates a miniaturized phase shifter based on slow-wave CPW and MEMS that occupy 0.47 mm2. A total phase shift of 152° was obtained with a maximum insertion loss of 3 dB, resulting in a figure of merit of 50°/dB at 60 GHz

Material parameter extraction algorithms are studied and simplified both for transmission-reflection and transmission-only methods. The simplified relations, which are closed-form in some cases, are analyzed to establish the uncertainty sensitivity coefficients and therefore, to clarify the main uncertainty contributions and reduce the systematic and random errors. Simple closed-form expressions presented

A new method for diagnosis of diabetes mellitus is proposed, which uses for measurement a lyophilized blood plasma sample prepared in the form of a pellet. The paper develops a methodology for fast spectroscopic measurements of such pellets with terahertz pulse time-domain holography. For that reason, blood plasma pellets were experimentally measured by terahertz time-domain spectroscopy system in

A waveguide modulator using switchable frequency selective surface (FSS) for amplitude shift keying modulation (ASK) at super high frequency (SHF) has been presented. The FSS consists of rectangular loop aperture elements with two PIN diodes at 180∘ intervals on every unit cell across the aperture. A minimum transmission isolation of 30 dB has been achieved at resonance frequency when the diodes are

Terahertz time-domain spectroscopy has been used for the characterization of different types of olive oil, such as extra virgin, pure, extra light, and pomace olive oils. Temperature-dependent refractive indices and absorption coefficients have been measured in 0.2–1.6 THz spectral-frequency range. Temperature-dependent Sellmeier coefficients and thermo-optic coefficients of these oil samples have

Composite materials made of micron-sized oxide particle fillers in an epoxy resin matrix that can be molded into desired shapes are widely used for packaging radiofrequency and microwave-integrated circuits (ICs). To potentially employ these materials with millimeter-wave ICs (MMICs), quantitative knowledge of the composites’ dielectric properties across a broad millimeter-wave band is necessary. Here

A multiple-joint transmission line based on the principle of the periscope was developed to realize the flexible guidance of terahertz (THz) waves. The transmission line has a slightly larger diameter than the standard plastic hollow-pipe waveguide, sufficient stability, low transmission loss, ultrabroadband spectrum, and low dispersion. The transmission line is evaluated using a THz time-domain spectrometer

The effect of frequency multiplication was investigated for a fundamental-harmonic 0.263-THz kW-level gyrotron, in which a certain fraction of its radiation was observed experimentally at the doubled operating frequency. Accurate measurements of the power of such high-frequency generation were carried out based on cyclotron absorption of radiation in a HgTe/CdHgTe quantum-well heterostructure. The

With ever increasing availability of terahertz fields, it is important to find suitable detection techniques without compromising the measured dynamic range. Electro-optic terahertz sampling techniques, which are commonly used to detect terahertz fields, exhibit over-rotation at high fields that limit the detection accuracy. Here we discuss a method to correct for over-rotation that put no limits on

The sub-200 cm−1 (sub-6 THz) vibrations of molecular crystals provide identifying features that are characteristic of each solid sample under study. These distinctive vibrational spectra have driven the development of new techniques and instrumentation in analytical spectroscopy. As terahertz time-domain spectroscopy and low-frequency Raman spectroscopy become increasingly prevalent in non-specialist

In a chirped pulse experiment, the strength of the signal level is proportional to the amplitude of the electric field, which is weaker in the millimeter-wave or submillimeter-wave region than in the microwave region. Experiments in the millimeter region thus require an optimization of the coupling between the source and the molecular system and a method to estimate the amplitude of the electric field

Among various applications of the gyrotrons to the fundamental physical research and to the high-power terahertz science and technologies, the material treatment based on the irradiation by millimeter and sub-millimeter waves is both one of the oldest and most advanced (industrial grade) technologies. In this paper, we present the recent advancements and the current status of both the development of

Wireless transmission of power from point to point has been developed in two predominate electromagnetic frequency ranges: near-infrared and microwave. In this paper, the prospect of wireless power beaming in the terahertz frequency range is explored with emphasis on the role of adverse weather. Link distance, power transmission, and safety performance of near-infrared, microwave, and terahertz power

As an initial step in developing steerable mirrors for terahertz (THz) wireless communication systems, this paper describes the development of a passive planar terahertz retroreflectors based on the Van Atta array. The retroreflector is optimized and simulated using finite-element modeling (FEM) software, fabricated via a low-cost additive manufacturing method, and characterized using THz time-domain

We observe an anomalously high electric field of terahertz (THz) radiation acting on a two-dimensional electron gas (2DEG) placed beneath a thin gold film, which, however, is supposed to be opaque at THz frequencies. We show that the anomalously strong penetration of the THz electric field through a very high conductive gold film emerges if two conditions are fulfilled simultaneously: (i) the film’s

The paper describes the development of passive, chipless tags for a novel indoor self-localization system operating at high mm-wave frequencies. One tag concept is based on the low-Q fundamental mode of dielectric resonators (DR) which exhibits peak scattering at its resonance frequency. As the radar cross-section (RCS) of DRs at mm-wave frequencies is far too low for the intended application, arrays

In this work, a high-pass waveguide filter with constant circular corrugations is presented. The proposed design allows propagation of HE11 mode which has similar Gaussian characteristics of the signals present in a fusion reactor. The device is designed to operate in W-band, i.e., 75–110 GHz, and it generates a wide passband of approximately 30 GHz. The internal corrugations in the proposed design

One of the major challenges in THz imaging using array detectors is the responsivity non-uniformities across different pixels. This is caused by different pixels responding differently and non-linearly to the same incident field. Unfortunately, such responsivity non-uniformities cannot be corrected by the traditional amplitude normalization method, which only accounts for linear responsivity. Therefore

We report the optical constants of the solid CO2 (dry ice) measured using terahertz time domain spectroscopy. The CO2 ice sample was grown by vapor deposition method. The optical constants were obtained by minimizing the amplitude of the oscillations of refractive index in the spectral domain. We found that the mean refractive index of CO2 ice at 10 K is 1.485 between 0.2 and 1.6 THz with a standard

Nowadays, terahertz and sub-terahertz frequencies are experiencing a significant interest from both academic and industrial world, since they offer a wide and unused spectrum available for different applications, as high-throughput communications, efficient imaging systems and medical uses. In this work an innovative sub-THz voltage-controlled oscillator (VCO) realized with a 130-nm SiGe process is

We present a time-of-flight tomography method for exceeding the naïve axial (i.e., depth) resolution limit of terahertz (THz) deconvolution by autoregressive spectral extrapolation (AR) based on the modified covariance method (AR/MCM). In contrast to Wiener filtering combined with wavelet denoising, AR/MCM does not discard any frequency components in the low signal-to-noise (SNR) regions of the measured

A polymer-based one-dimensional photonic crystal with a defect mode was demonstrated for the terahertz frequency range. The photonic crystal was designed to achieve a photonic bandgap centered around 100 GHz with a narrow defect mode at the center frequency. The defect mode allowed a narrow band transmission at the center of photonic bandgap, while the transmitted signal was suppressed in the rest

The low-frequency (terahertz) dynamics of condensed phase materials provide valuable insight into numerous bulk phenomena. However, the assignment and interpretation of experimental results require computational methods due to the complex mode types that depend on weak intermolecular forces. Solid-state density functional theory has been used in this regard with great success, yet the selection of

The objective was to investigate the clinical course of ocular damage and the healing process in eyes exposed to 162 GHz millimeter wave (MMW). As a 162-GHz electromagnetic wave source, a gyrotron FU CW GV was used. An ocular damaged rabbit model with good reproducibility for 162 GHz MMW exposure was developed, and damage occurrence threshold values were obtained. The right eyes of pigmented rabbits

This paper discusses advances related to the integration of future mobile electronic THz systems. Without claiming to provide a comprehensive review of this surging research area, the authors gathered research on selected topics that are expected to be of relevance for the future exploration of components for practical mobile THz imaging and sensing applications. First, a brief technology review of

In this paper, a broadband and compact oversized rectangular waveguide transition is proposed. Employing novel quadruple-ridged waveguide technology, two quadruple-ridged waveguides achieve an extreme compactness interconnection from a standard rectangular waveguide to an oversized rectangular waveguide. This design can be used as an alternative way to create a new oversized rectangular waveguide transition

Dielectric materials play a supporting role for electronic circuits. With the development of 5G millimeter wave communication, precision measurement of dielectric property becomes increasingly important. This paper introduces a free-space quasi-optical spectroscopy for complex dielectric property measurement. This spectroscopy can work in both transmission and reflection modes to accommodate both low-loss

We present an analysis of graphene-loaded transmission line switches for sub-millimeter wave and terahertz applications. As such, we propose equivalent circuit models for graphene-loaded coplanar waveguides and striplines and examine the switching performance under certain parameters. Specifically, we identify the optimum design of graphene switches based on transmission line characteristic impedance

Strontium molybdate (SrMoO3) thin films are grown epitaxially by pulsed laser deposition onto gadolinium scandate (GdScO3) substrates and characterized in the terahertz (THz) and visible part of the electromagnetic spectrum. X-ray diffraction measurements prove a high crystallinity and phase-pure growth of the thin films. The high-quality SrMoO3 thin films feature a room temperature DC conductivity

A novel Ka-band azimuthal supported angular log-periodic strip-line (ASALS) slow wave structure (SWS) is proposed for a miniature radial sheet beam traveling wave tube (TWT). In the proposed SWS, two dielectric rods are employed to support the ASALS at both azimuthal sides. The strip-line is made of high-melting metal; thus, the ASALS SWS has a higher power capacity than microstrip SWSs. The high-frequency

Currently semiconductor lasers in the wavelength range from 20 to 60 μm are scarce. HgTe/CdHgTe heterostructures is a potential basis for alternative sources of coherent radiation in this range. We propose that in such structures carrier heating is the main mechanism, which quenches stimulated emission under high excitation intensity. Lower-energy optical excitation is one way to reduce this negative

Sensitive millimeter wave diagnostics in magnetic confinement plasma fusion experiments need protection from gyrotron stray radiation in the plasma vessel. Modern electron cyclotron resonance heating (ECRH) systems take advantage of multi-frequency gyrotrons. This means that the frequency band of some millimeter wave diagnostics contains more than one narrow-band gyrotron-frequency line, which needs

A liquid crystal (LC)-based double dipole terahertz phase shifter is proposed. The block model is utilized in simulations to analysis the influence of inhomogeneity of the LC substrate. The sensitive parameters of the double dipole are simulated and analyzed. An array consisting of 30 × 30 patch elements is designed and fabricated. Experimental results exhibit that the phase shift is over 360° in the

By focusing a femtosecond laser beam onto the lateral face of a periodically poled KTP crystal, we generate a THz pulse through optical rectification of the laser pulse. The THz signal is recorded by means of a common THz time-domain technique, which allows us to obtain both the magnitude and sign of the THz waveform, and then the magnitude and phase of its spectral components thanks to a numerical

The design of a magnetron-injection gun (MIG) suitable for using in the CW 3-rd harmonic gyrotron with an output frequency of 1.185 THz and an output power about 100 W, intended for DNP/NMR spectroscopy applications is described. To improve the mode selection, several electron optics schemes are investigated. The MIG allows using both single-beam and double-beam schemes of the gyrotron operation with

High capacity radio lines operating in the sub-THz and THz ranges often require very efficient optical elements with a focal length to an aperture diameter ratio—f-number—less than 1. Here, we propose a new type of double-sided sub-THz focusing diffractive optical element with f-number equal to 0.2, designed for quasi-monochromatic illumination with carrier frequency equal to 170 GHz. The element is

To meet increasingly demanding technological needs in modern security and industrial applications involving rapid close-range screening, we have developed a 100-GHz linear scanner. Having incorporated a novel approach in terahertz sensing and an advanced IMPATT-diode signal generating technique, the proposed system offers an efficient non-destructive testing (NDT) solution that is absolutely safe,

In this paper, we measure broadband terahertz spectra from a single 744-nm filament produced in tight, medium, and loose geometrical focusing conditions. Terahertz spectra are measured using interferometer coupled to a helium-cooled bolometer avoiding any cutoff frequencies. Based on THz spectrum maximum position and spectral width, we estimate electron-heavy particle (neutrals and ions) collision

Equi-distantly distributed multi-peak frequency spectrum was observed in a high-power 300-GHz band gyrotron for the case of strong reflection off the vacuum window. An oscillation mode different from the design mode can oscillate by adjusting the magnetic field in the cavity. However, a large fraction of the output wave is reflected by the vacuum window. The reflected wave returns to the cavity through

This paper studies a continuous atmospheric-pressure discharge maintained by focused subterahertz radiation of a 263-GHz gyrotron. A plasma torch propagating toward microwave radiation was sustained on an argon flow exiting a metal gas tube in the surrounding atmosphere of air. Using a high-speed camera, the spatial structure of the torch was studied, and the temporal dynamics on timescales of the

We identify experimental conditions for efficient generation of THz pulses by high power near IR laser radiation: 2 TW, 30 fs, 800-nm laser pulses with their second harmonic were slightly focused in a low-pressure gas cell in such a way to avoid multiple filamentation and excessive ionization. This two-color scheme yields a microjoule level of THz pulses which is two orders of magnitude higher than

The impact of the response speed of a microelectromechanical system (MEMS) bolometer on the quality of terahertz (THz) imaging with rapid scan has been investigated and compared with a pyroelectric detector (PED). The imaging system was an active imaging composed of the MEMS bolometer, THz quantum cascade laser, and two-dimensional translation stage. The scanning process of the imaging system consisted

Abstract We report on the observation of terahertz (THz) radiation induced band-to-band impact ionization in HgTe quantum well (QW) structures of critical thickness, which are characterized by a nearly linear energy dispersion. The THz electric field drives the carriers initializing electron-hole pair generation. The carrier multiplication is observed for photon energies less than the energy gap under

Abstract We propose a broadband end-fire antenna for continuous-wave terahertz (THz) photomixing–based devices working in the frequency range of 0.5–1 THz. A compact Vivaldi antenna is presented that does not require any hyper-hemispherical silicon lens to collect and collimate THz radiation unlike the conventionally used broadside antennas. The antenna is tailored to radiate THz into or receive radiation

Abstract We detail the design and characterization of a terahertz range achromatic quarter-wave plate based on a stack of aligned variable thickness birefringent sapphire discs. The disc thicknesses and relative rotations of the discs are determined through a basin-hopping Monte Carlo thermal annealing routine. The basin-hopping scheme allows an improved refinement of the required thicknesses and rotations

Abstract In response to the urgent demand for efficient, safe, and speedy imaging in remote security screening applications, a new sub-terahertz security body scanner has been developed. Integration of innovative THz sensing technique and advanced IMPATT-diode-based signal-generating technology resulted in a cost-effective cutting-edge system capable of real-time visualization of the threats hidden

Abstract The main reason for the alternation of terahertz (THz) response in biological samples is the transition of a part of water from its free to bound state and back. To analyze such results, a precise spectrum of bound water within THz range should be known. The suggested wet powder spectroscopy method is optimal for this task. We measured the THz transmission of dry glucose pressed into pellets

The original article contains error in one of the author family names John Koulakisf should read as John Koulakis.

Abstract We present the results of recent IAP RAS investigations, which were aimed at controlling the radiation frequency and spectrum of THz-range medium-power gyrotrons. Problems of extending the smooth frequency tuning band and providing high-frequency stability in CW regimes are discussed. The development of gyrotrons with stated parameters are of interest for many modern applications, including

Abstract A sub-THz, second harmonic, multifrequency gyrotron, Gyrotron FU CW GVII, which radiates Gaussian beams, was developed. This device was designed to change the frequency in a stepwise manner in the range from 270 to 420 GHz. In this paper, we present the first experiments conducted using this gyrotron. Nine modes were selected for this study. The oscillation frequency of the selected modes

Abstract A polymer-based one-dimensional photonic crystal with a photonic bandgap in terahertz frequency range was designed and fabricated through stereolithography and was characterized using THz spectroscopy. The photonic crystal studied here consists of alternating compact and low-density layers. The compact layers were fabricated from fully polymerized polymethacrylate without any intentional internal

Abstract We have demonstrated a method for active modulating terahertz wave using CsPbBr3 perovskite quantum dots (QDs)–embedded double-C metallic metamaterial unit cells. The resonance response frequency of the proposed CsPbBr3 perovskite QDs-embedded metamaterial can be tuned by varying the external applied photoexcitation intensity. By doing so, we measured the dynamic terahertz wave transmission

Abstract Terahertz (THz) absorption spectra of cross-linked polyurethane films were observed at 30–180 °C. The obtained spectra displayed characteristic absorption bands. A band observed at 2.6 THz was assigned to the C=O···N-H hydrogen bond vibration using previously reported data. DFT calculation results confirmed that a band at 7.5 THz arises owing to the torsional vibration of cross-linked molecules

Abstract We have constructed a numerical model for injection-seeded terahertz-wave parametric generators in which the pump depletion, the duration of the pump pulse, as well as the spatial modes of the pump and seed beams are taken into consideration. Compared with other models which only provide the parametric gain under the assumption of low pump depletion, our model can make the predictions on the

Abstract Using terahertz time-domain spectroscopy, the frequency-dependent conductivities of polyaniline emeraldine salt-polyethylene (PAni-PE) pellets were measured at different mass concentrations. THz conductivities were compared to the behavior of DC conductivities measured using impedance spectroscopy. The DC conductivity behavior with mass concentration showed a low percolation threshold. The

Abstract This paper presents a D-band (110–170 GHz) transmitter/receiver (Tx/Rx) chipset with end-fire on-chip antennas (OCAs) using 0.13-μm SiGe BiCMOS technology. The input LO signal frequency of the chipset is 31.25 GHz. A 62.5-GHz frequency doubler, a D-band 2nd-harmonic up-conversion mixer, a power amplifier (PA), and an end-fire antenna are integrated in the Tx. An end-fire antenna, a D-band

Abstract Acousto-optic modulation of terahertz free-electron laser radiation was investigated using diffraction on an acoustic wave in liquefied sulfur hexafluoride at room temperature. At the wavelength 130 μ m, the diffraction efficiency in Bragg regime of interaction 1% was obtained at 75 V driving electrical signal applied to the transducer terminals.

Abstract This paper reports for the first time on a micromachined interposer platform for characterizing highly miniaturized multi-port sub-THz waveguide components. The reduced size of such devices does often not allow to connect them to conventional waveguide flanges. We demonstrate the micromachined interposer concept by characterizing a miniaturized, three-port, 220–330-GHz turnstile orthomode

Abstract The quality of sunflower seed usually influences the load and product quality. The plumpness, expressing as the percent of the kernel and shell (%), is a crucial indicator reflecting the vigor of the sunflower seed. Investigations were carried out to measure the plumpness of intact sunflower seed by the use of terahertz (THz) transmittance imaging. The THz data of the worms, defects, and sound