The capability for actual measurements-not just simulations-of the dynamical behavior of THz electromagnetic waves, including interactions with prevalent 3D objects, has become increasingly important ...not only for developments of various THz devices, but also for reliable evaluation of electromagnetic compatibility. We have obtained real-time visualizations of the spatial evolution of THz electromagnetic waves interacting with a single metal micro-helix. After the micro-helix is stimulated by a broadband pico-second pulse of THz electromagnetic waves, two types of anisotropic re-emissions can occur following overall inductive current oscillations in the micro-helix. They propagate in orthogonally crossed directions with different THz frequency spectra. This unique radiative feature can be very useful for the development of a smart antenna with broadband multiplexing/demultiplexing ability and directional adaptivity. In this way, we have demonstrated that our advanced measurement techniques can lead to the development of novel functional THz devices.
We demonstrate the possibility of inspection of chemical mixtures by terahertz (THz) spectroscopic imaging using known spectral data of the pure chemical components. This method, which is based on ...principle component analysis, can determine the existence of chemicals, identify them, map the spatial distribution of each component, and measure their content in a target. We determined qualitatively and quantitatively the components not only in pure chemical samples but also in mixtures. The content of each component determined experimentally comes in agreement with their respective known contents.
The measurement of water concentration and distribution in thin biotissues with terahertz (THz)-wave has been proposed. In this paper, a novel sample preparation approach was introduced to ...effectively preserve tissue freshness at room temperature. Excellent stability of this method was demonstrated by measuring the transmittance spectroscopy and imaging many times within a certain time. Moreover, the reliability of water volume concentration measurement with THz-wave was evaluated. Measurement results using THz-wave were in good agreement with volume concentration measurement results based on other quantitative methods. The results suggest that water concentration and distribution measurement in thin biotissues using THz-wave will be a potential modality for medical and biological diagnosis.
A new type of flexible terahertz-wave hollow waveguide has been developed using ferroelectric polymer poly vinylidene fluoride (PVDF) as the cladding material. The transmission efficiency of the PVDF ...waveguide was better than a metal hollow waveguide with the same size and structure as the PVDF waveguide. This paper also reports the bent-angle dependencies of the transmission efficiency of the hollow PVDF.
This paper describes a high efficiency (68%), high output power (100 W), high reliability GaN HEMT amplifier for C-band space applications. The high efficiency is achieved by 2nd-harmonic frequency ...(2f o ) tuning circuits in the input and output matching circuits. The input circuit uses open-ended stubs located nearby FET gate terminals for setting the 2f o reflection-phase at the optimum phase. In the output circuit, the optimum 2f o reflection phase is realized using three transmission-line transformers while matching loss is kept low at fundamental frequency. In addition, a 3000 hour's RF overdrive life test reveals that an estimated mean time to failure (MTTF) is 1×10 7 hours at 150°C channel temperature, proving that the amplifier has sufficient reliability for space applications. To the best of our knowledge, the efficiency of 68% is the highest of 100-W class C-band amplifiers ever reported, and is also comparable to that of commercially available traveling wave tube amplifiers.
A review to our effort on developing the transform-limited, frequency-agile terahertz-wave parametric generator (TPG) is presented. A frequency-agile THz-wave generation is realized by introducing ...the injection-seeding method and the optical design for the stationary dispersion-compensation The purity of the THz-wave frequency was dramatically improved to Δv/v<10−4. Simultaneously, the THz-wave output was several hundred times higher than that of a conventional TPG. In addition, a wide frequency tuning with fast tuning speed were realized. The THz-wave frequency can be set randomly or scanned continuously over a frequency range from 0.6 THz to 2.4 THz with narrow linewidth of sub 100 MHz. Furthermore, a tabletop, high-performance THz-wave gas spectrometer based on this achromatic injection-seeded TPG was developed. To demonstrate the potential of this system, we performed the measurement of the absorption line due to rotational transitions of the water molecules and determined their pressure-broadening coefficient.
We propose a surface-emitted cavity configuration for a terahertz-wave parametric oscillator that allows THz wave emission perpendicular to the crystal surface without any output coupler. The ...oscillating idler and pump waves are reflected at the surface of a nonlinear crystal in a single resonance cavity, satisfying the noncollinear phasematching condition. The radiated THz wave has a Gaussian profile. The measured beam quality factors (M(2)) were 1.15 and 1.25 in the horizontal and vertical directions, respectively. The measured tunable range was 0.8-2.74 THz. A test of transmission imaging using a test pattern was demonstrated.
► Ultrahigh sensitive terahertz detectors based on asymmetric dual-grating-gate HEMT. ► A record responsivity of 2.2kV/W at 1THz with a superior low noise equivalent power of 15pW/√ãHz. ► Strong THz ...photocurrent is first generated by the nonlinearity of the plasmon modes. ► The THz photovoltaic response is read out at high-impedance parts of 2D channel. ► Asymmetry of the cavity boundaries enhances the responsivity by more than two orders of magnitude.
We report on ultrahigh sensitive, broadband terahertz (THz) detectors based on asymmetric dual-grating-gate (A-DGG) high electron mobility transistors, demonstrating a record responsivity of 2.2kV/W at 1THz with a superior low noise equivalent power of 15pW/√Hz using InGaAs/InAlAs/InP material systems. When THz radiation is absorbed strong THz photocurrent is first generated by the nonlinearity of the plasmon modes resonantly excited in undepleted portions of the 2D electron channel under the high-biased sub-grating of the A-DGG (as a quadratic nature of the product of local carrier density and velocity perturbations), then the THz photovoltaic response is read out at high-impedance parts of 2D channel under the other sub-grating biased at the level close to the threshold. Extraordinary enhancement by more than two orders of magnitude of the responsivity is verified with respect to that for a symmetric DGG structure.
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