In this work, we have investigated the nonreciprocal transmission of a terahertz (THz) isolator based on the magneto-metasurface. A structured InSb layer coats on the silica substrate in which the numerical simulation shows that this metasurface has isolation over 60dB at 0.646 THz and a 10dB operating bandwidth of 13 GHz under an external magnetic field of 0.3T with an insertion loss less than 2.5dB. Importantly, we have discussed the necessary conditions to form THz nonreciprocal transmission in the magneto-metasurface, which closely depends on the magneto-optical material and the relations of the structure asymmetry, wave polarization direction and external magnetic field direction. Moreover, the isolation dependences and tunability of this device on the external magnetic field have also been investigated, which shows the best operating state with a high isolation can be well designed for the device. This kind of low-loss, high isolation, easy coupling THz magneto-metasurface isolator has broadly potentials for THz application systems.

We have designed, fabricated and measured localized surface plasmon resonance (LSPR) based monopole nano-antenna coupled photo-conductive antennas (PCAs) for THz-time domain spectroscopy (TDS) systems. LT-GaAs material was used to fabricate the THz PCAs. The performance of the nano-antenna coupled PCAs was compared to the standard PCAs. The THz signal level has increased by a factor of 2 by using the plasmonic monopole nanoantenna.

III-Nitride semiconductors having huge longitudinal optical phonon energies are promising as materials to solve a problem of "development of operational frequency range (5-12 THz)" on terahertz quantum cascade lasers (THz-QCLs). In this study, for the purpose of realization of THz lasing due to optical transition between target levels, we designed and fabricated THz-QCLs with unique quantum cascade (QC) structures named “Pure 3-level laser system”. We successfully for the first time observed lasing action emitting at the same frequencies (5.5 and 7.0 THz) as the target ones from GaN-based THz-QCL devices. We also successfully opened up new frequency region on THz-QCLs.

We demonstrate a new approach to visualize the distribution of molecular adsorbates on graphene using terahertz emission spectroscopy and imaging. We found that the waveforms of terahertz radiation from graphene-coated InP sensitively changed with the type of the atmospheric gas, the laser illumination time. The change of waveforms is explained through band structure modifications in the InP surface depletion layer due to adsorbed oxygen. These results demonstrate that terahertz emission serves as a local probe for monitoring adsorption and desorption processes on graphene, suggesting a novel two-dimensional sensor for detecting local chemical reactions.

This talk will illustrate some new concepts in the area of hybrid metamaterials, metamaterials that are embedded with active circuit elements such as transistors for applications in modulation and detection at terahertz frequencies.

Two types of zero-biased InGaAsP Schottky barrier diode (SBD) detectors were developed. A J-band rectangular-waveguide-input module was fabricated to improve the sensitivity by implementing an SBD integrated with a resonant matching circuit. It showed a peak sensitivity of 1460 V/W at around 350 GHz. A quasi-optical module that implements an antenna-integrated SBD was fabricated for broadband operation with linear polarization characteristics. It could detect signals at frequencies from 30 GHz to 1 THz. The polarization angle was stable with a degree of polarization larger than 95 % at frequencies from 80 to 600 GHz.

We report a terahertz (THz) wave amplifier based on optical parametric processes in magnesium-oxide-doped lithium niobate (MgO:LiNbO3) crystals. The amplifier operates at room temperature and has a gain of 55 dB. This system comprised an injection-seeded THz wave parametric generator and amplifier, both of which employed MgO doped LiNbO3 crystals. Both the emitter and amplifier crystals were pumped by a microchip Nd:YAG laser.

Recent progress in our room-temperature resonant-tunneling-diode (RTD) terahertz (THz) oscillators and HEMT THz receivers are reported. Oscillations up to 1.55THz were obtained using optimized antenna and RTD. Using two-element oscillator array, high output power of 0.6mW at 620GHz was obtained. THz communications up to 3Gbps were demonstrated. A structure for high-speed direct modulation was fabricated, and the intensity modulation up to 30GHz was achieved. A novel oscillator structure was proposed and fabricated for extraction of output power without using Si lens. We fabricated a HEMT detector integrated with broadband bow-tie antenna, and achieved high current sensitivity of ~5A/W at 280GHz.

We demonstrated the first room temperature single mode THz emission with a stable frequency output and narrow linewidth at 4.1 THz with different currents and temperatures by using a composite distributed feedback (DFB) waveguide. This is desirable in many applications, such as imaging, and astronomical research. We currently hold the THz power record of this type monolithic THz sources with 1.9 mW at 3.5 THz in pulsed mode operation by using single-phonon resonance design, Čerenkov phase matching scheme, and epi-down mounting scheme. We demonstrated the first room temperature continuous wave THz QCL source with power of 3 W at 3.6 THz with buried ridge waveguide. We demonstrated broad, monolithic spectral coverage (1-4.6 THz) and high peak power at room temperature using narrow linewidth integrated sources and Čerenkov phase-matching. Very recently, we achieve the widely electrically tunable room temperature THz emission with continuous frequency tuning range of 2.6-4.2 THz by using a multi-section DFB waveguide geometry.

Heterodyne receivers based on Schottky barrier diodes offer excellent performance for a range of scientific and commercial applications, including atmospheric studies, plasma diagnostics, communications, imaging and test & measurement systems. These receivers have excellent sensitivity and bandwidth and operate at room temperature. This paper will describe VDI's efforts to fundamentally reduce the size and weight of these receivers so that they can be used in a wider variety of applications. The talk will focus on the development of a W-Band receiver for a NASA cubesat and a ~300GHz receiver for the ITER ECE system.

A novel polarization rotator design for the mid-IR region is reported by using silicon-on-insulator technology. We also report 90% polarization conversion for a 536 m long device by using rigorous full-vectorial numerical approaches.

Small and fast objects, like bullets of caliber 4.5 to 8 mm, fired from guns like AK-47, can cause serious problems to aircrafts at asymmetric warfare. Especially slow and big aircrafts, like heavy transport helicopters are an easy mark of small caliber hand fire weapons. These aircrafts produce so much noise, that the crew often cannot recognize an attack unless important systems of the aircraft fail. This is just one of many scenarios, where the detection of fast and small objects is desirable. Another similar scenario is the collision of space debris particles with satellites. To detect such objects by a radar system, several issues have to be taken into account. First of all, the radar equation, which calculates the maximum range, has to be interpreted carefully. As the bullet diameter is in the order of or smaller than the radar wavelength, the radar cross section (RCS) of a sphere is no longer only a function of geometry. Assuming a 5 mm sphere the RCS decreases with the power of 4 by the wavelength. Increasing the frequency beyond 16 GHz enters the so called Mie region, where the RCS is hard to predict caused by interference effects. Further increasing the frequency decreases the Mie effect. Not till then a frequency of 190 GHz is reached, the instable Mie region is left and a stable RCS of -47 dBsm can be assumed. At our contribution we will also focus on extreme linear and fast chirp generation with high bandwidth for FMCW-radars. Also we will present results on MMICs we have developed for radar applications at W-Band (75-110 GHz) and H-Band (220 – 325 GHz). First experimental results will be also presented.

Metasurface analogues of electromagnetically induced transparency and absorption are experimentally observed in near-field coupled subwavelength systems. Engineered with active control mechanisms, the unique resonances are promising in next-generation chip-scale terahertz photonic devices.

Electromagnetic metamaterials (MMs) consisting of highly conducting sub-wavelength metallic resonators enable many unusual electromagnetic properties at designed frequencies which are not permissible with the naturally occurring materials. The electromagnetic properties of metamaterial are typically controlled by the clever design of the MM unit cell, often termed as meta-molecule, consisting of metallic split ring resonators (SRRs) or meta-atoms. The near field coupling between meta-atoms plays a vital role in tuning the natural resonances of individual SRR and, therefore, has the ability to modify the far-field radiative properties significantly. It is shown that near field coupling between the meta-atoms could lead to resonance tuning, mode splitting, and ultrafast switching in passive and active resonators. In this article, we present a brief review on tuning the metamaterial properties by active and passive manipulation of near field coupling between neighboring split ring resonators.

In this paper we investigate the effects of subwavelength antenna resonator element dimensions on the anomalous reflection properties of metasurfaces operating in the millimeter-wavelength and terahertz frequency regions. Such two-dimensional structures are finding uses as flat optics in a variety of applications including beam steerers, reflectarrays, and broadband, polarization-independent radar absorbers. Numerical simulations were performed to characterize the reflection phase-shift of rectangular resonators of varying dimensions for efficient metasurface and reflectarray design. We show that antenna elements with deeply-subwavelength thickness provide the largest total phase variation and therefore present a viable design methodology for a variety of high frequency applications.

- invited talk - We use intense, phase-locked, few-cycle terahertz pulses at photon energies far below electronic interband resonances and peak amplitudes of 72 MVcm-1 to drive the coherent interband polarization and dynamical Bloch oscillations in semiconducting gallium selenide. The dynamics entail generation of strong high-harmonic transients spanning the entire terahertz-to-visible spectral domain between 0.1 and 675 THz in a single, phase-locked pulse, exploring charge transport at optical clock rates. Furthermore, we explore high-field transport at 1 THz exploiting the near-field enhancement in metamaterials, leading to nonperturbative terahertz nonlinearities and an interband Zener tunneling rate exceeding previously reported values by 10 orders of magnitude.

The most powerful and frequency agile sources of continuous wave power in the frequency range near 1 THz are built with diode based frequency multiplier chains. This paper will overview VDI's recent development of improved sources for these applications. This will include a description of an improved 264GHz source for DNP experiments with 90mW output power and an overview of the ongoing development of sources for radio astronomy at 1.9THz.

Second-order nonlinear optical wavelength-conversion has been attractive for generating intense terahertz (THz) wave by optical parametric mixing, and for THz-wave detection by up-converting from THz wave to near infrared light. Using LiNbO3, kilowatt peak-power THz-wave radiation and sensitive THz-wave detection down to several tens of atto-joule using LiNbO3 or DAST crystals have been demonstrated. Especially, the up-conversion detection working at room temperature is more than that of cryogenically cooled THz detector. The sensitive THz-wave detection leads to a novel design using slant-stripe-type periodically poled LiNbO3 for practical use. The nonlinear optical up-conversion detection is promising and broadening THz horizons.

Terahertz kinetics spectroscopy under high speed acquisition of reflected energy is an effective tool for layered materials’ deformation characterization under ballistic impact. An effort is outlined here that is aimed at utilizing the kinetics spectrum for deducing quantities that uniquely describe a ballistic impact event, such as deformation, velocity and energy. Additionally, the same technique may be utilized for real-time assessment of trauma or concussion by measuring the helmet wore by an athlete as opposed to diagnosis by a biomarker; since biomarker’s threshold depends on an individual’s genetic and physiological make up and may vary widely from person to person.

Water is a major component of the atmosphere and will dominate the propagation of terahertz radiation. This study will present results of high-resolution broadband measurements of the terahertz atmospheric absorption and detail the technique for directly measuring the pressure broadening coefficients, absolute absorption coefficients, line positions, and continuum effects. The same technique was used to measure the line parameters for methanol, an atmospheric trace gas of interest. The data obtained in the study will be of immediate use, as it is uncommon to simultaneously measure these parameters. Differences between the measured data and those in databases will be discussed.

We show possibility of the detection and identification of substance at long distance (several metres, for example) using the THz pulse reflected from the object under the real conditions: at room temperature and humidity about 70%. The main feature of this report consists in a demonstration of the detection and identification of substance using the computer processing of the noisy THz pulse. Amplitude of the useful signal is less than the amplitude of a noise. Nevertheless, it is possible to detect “fingerprint” frequencies of substance if both these frequencies are known and the SDA method is used together with new assessments for probability estimation for presence of detected frequencies. Current results show feasibility of using the THz pulsed spectroscopy for the counter-terrorism problem.

The Dirac-like electronic dispersion relation (linear energy vs. momentum) in solids is a topic of current interest in the scientific community. This unique linear dispersion could be beneficial for the design of more efficient devices for both electronic and optoelectronic purposes. We have used THz magneto-photoresponse spectroscopy to probe the gapped Dirac-like dispersion relation of the two-dimensional electron gas of HgTe quantum wells with well width ( 6.1 nm) such that the topmost valence and conduction bands have the conventional band alignment of found in zinc blende direct gap semiconductors. Several interesting physical mechanism including Rashba effect, magneto-thermoelectric properties of such a system will be presented.

Terahertz (THz) detector working at room-temperature (RT), consisting of a Nb5N6 thin film microbridge and a dipole planar antenna, is reported. Due to the high temperature coefficient of the resistance (TCR), which is as high as -0.7% /K, of the Nb5N6 thin film, such an antenna-coupled microbolometer is quite suitable for detecting THz signals. Previously, THz detectors working at 0.1 THz have been reported. Here, the results around 0.3 THz will be presented.

Two types of terahertz (THz) cameras with an enhanced sensitivity in sub-THz region are developed, which incorporates 640x480 or 320x240 uncooled microbolometer-type THz focal plane array (FPA) with a pixel pitch of 23.5 m. The THz-FPA has the new pixel structure which has several times longer optical-cavity length than the conventional pixel has, so that the Minimum Detectable Power per pixel (MDP) is improved ten times in sub-THz region, especially 500-600 GHz. Images of both transmission and reflection are presented, using 500 GHz source, a collimator lens, Galvano mirrors, two wire grids and a quarter-wave plate.

Development of infrared and sub-terahertz radiation detectors at the same sensitive elements on the base of mercury-cadmium-telluride (MCT) are reporteded. Bi-color un-cooled and cooled to 78 K narrow-gap MCT semiconductor thin layers grown by liquid phase epitaxy or molecular beam epitaxy procedure on CdZnTe or GaAs high, resistivity substrates with bow-type antennas were considered both as sub-terahertz direct detection bolometers and 3 to 10 um infrared photoconductors. Their room temperature noise equivalent power (NEP) at frequancy ~ 140 GHz and signal-to-noise ratio (S/N) under the monochromatic (spectral resolution of ~0.2 um) globar illumination were reached NEP ~5*10^-10 W/Hz^1/2 and S/N~50, respectively.

In this work different approaches to recognizing concealed, dangerous substances are considered. Analyses are performed on measured THz spectra. Ideally, an approach should not be sensitive to measurement conditions. On the other hand, it should be specific. These issues, as well as, false alarm rates are considered when approaches are compared.

Exelis Geospatial Systems and its CEIS partners at the University of Rochester and Rochester Institute of Technology are developing an active THz imaging system for use in standoff detection, molecular spectroscopy and penetration imaging. The current activity is focused on developing a precision instrument for the detection of radiation centered on atmospheric windows between 200 GHz and 400 GHz (available sources). A dark field camera is developed to image the scattered energy produced from actively illuminating objects with semi-coherent non-ionizing radiation. The optical prescription consists of a catadioptric f/n 1.43, 1-to-1 imager with an aperture of 0.455 m intended to achieve a resolution of 3.0 mm (200 GHz) at a standoff distance of 1.0 m. The primary goal of the initial system development is to produce a precise scientific instrument for THz technology development positioned in the electromagnetic spectral range between 188 GHz and 7.0 THz. Scatter image measurements are presented in order to verify image formation as well as estimate the instruments ability to penetrate materials.

This work investigates the possibilities of measuring key mechanical and electrical properties of silicon semiconductors with terahertz (THz) waves. Time-domain THz tomography mappings were used for contactless precision determination of wafer thicknesses, flatness/warpage and deformation shapes under different mechanical loads and validated against numerical simulations. In parallel, THz spectroscopy was used to reliably measure carrier dynamics of optically injected charges in low doped silicon, as used in particular in the photovoltaics industry. Time-domain THz tomography and spectroscopy thus have great potential for the inspection of mechanical and electrical properties of Si-based semiconductors, in particular due to their non-invasive nature.