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Intermediate frequency (IF) gain bandwidth (GBW) of terahertz (THz) heterodyne detectors based on superconducting niobium nitride (NbN) hot electron bolometers (HEBs) has been studied in details. Two different methods, resulting in same IF GBW value of about 3.5 GHz are reported here.
Nanomaterials exhibit unique properties and have been receiving considerable interest. The dielectric measurement has been performed on gold nanoparticle dispersions by using a THz-Time domain spectroscopy system to investigate the interaction of THz waves with gold nanoparticles.
Scaled radar cross section measurements are a commonly employed tool in civil and military aviation. We propose a flexible setup which makes use of a fiber-coupled THz time domain spectrometer and a two circle goniometer. Measurements are performed on reference objects and on scale model aircraft.
The single metal wire (SW) is experimentally verified to be an competitive terahertz(THz) transmission line. Making use of the Modified Drude Model (MDM) based on the Sommerfeld theory, the transmission behaviors of Surface Plasmon Polaritons(SPPs) along SW are systemically investigated theoretically for axial symmetric and asymmetric modes. Some important physical phenomena are discussed, and the...
Influences of parameters on the nonlinear power are simulated by using a Hamiltonian model. Results show that the saturation power is mainly determined by the mismatched parameter, and optimum of the mismatched parameter increases the saturation power and shortens the saturation-interaction length. Also, higher beam current leads to a higher saturation power and shorter saturation-interaction length.
We present electrical rectification up to 300 GHz with novel asymmetric nanochannels realized for the first time on AlGaN/GaN material system. At zero bias, sensivities of 100 V/W/Hz1/2 are obtained at room temperature.
Absorption spectra of smoke produced from polyvinyl chloride (PVC) and molded charcoal at high temperature are investigated between 500 and 950 GHz. Observed peaks at 626 GHz for PVC and at 692 and 921 GHz for molded charcoal are respectively assigned as the spectral signature of hydrogen chloride and carbon monoxide contained in smoke. Smoke from molded charcoal also showed absorption peaks of hydrogen...
In the paper we show that under the excitation of a line current, a dielectric medium loading in the lower half-space of the sub-wavelength holes array brings surprising changes to the diffraction radiation. In the lower half-space, the surface wave becomes a radiation wave. The fundamental space harmonic is transformed into Cherenkov radiation with unique characteristics and the first negative space...
We demonstrate the ultra-fast detection of terahertz pulses from a quantum cascade laser (QCL) using superconducting NbN and YBCO detectors. This has enabled both the intrapulse and interpulse dynamics of a THz QCL to be measured directly, including interpulse heating effects on sub-µs timescales.
Passive millimeter-wave microscopy that enables imaging of the thermal radiation emitted from a viewed sample with a spatial resolution below the diffraction limit is investigated. Experiments performed at 50 GHz (λ = 6 mm) at various sample temperatures demonstrate the feasibility of our passive millimeter-wave microscope to image thermal radiation even in the low temperature range where passive...
We have developed the λ/4 phase-shifted 1.3-µm dual mode laser as an optical beat source of continuous-wave (CW) terahertz (THz) generation. The mode beat frequency is continuously tuned from 230 to 1485 GHz via integrated micro-heaters. The CW THz system is also demonstrated with low-temperature-grown InGaAs photomixers.
While most scientific experiments take place in a controlled laboratory environment systems for industrial applications have to cope with instable temperatures. We investigate the performance of InGaAs/InAlAs THz antennas for the temperature from −20 to 80 degrees Celsius.
We demonstrate the concept of an anti-rod dimer planar metamaterial with strong birefringence and optical activity in the THz range. The retrieval of circular transmission components shows an asymmetric transmission effect for right-to-left and left-to-right polarization conversion.
This study proposes a theory to separately diagnose the beam-wave dynamics of backward wave (BW) and forward wave (FW) interactions in the frequency-tunable gyrotron. It is clarified that the BW interaction would dominant the feedback mechanism regardless of the cavity structure resonance. The FW interaction effect is found to be minor in small signal regime but critical in the large signal regime...
In this paper, the dumbbell resonant cavity frequency tuning method and beam wave interaction system of W band sheet beam Klystron (WSBK) has been studied. Under the designed value of beam voltage 75kV, beam current 3.8A, and beam size of 10*0.5 mm2, the structures and high frequency parameters of single gap and multi-gap cavities are tested and discussed to achieve the higher output power in detail...
Terahertz absorption spectra were measured for nylon-6/6, nylon-6, nylon-11 and nylon-12 by Fourier transform far-infrared spectroscopy. Different spectral features among the four species were interpreted as the characteristics of crystalline conformations of nylons.
We performed terahertz time domain spectroscopy on erbium orthoferrite. The spin reorientation transition was observed as switching of magnetic radiation mode between F and AF mode, and the change in the polarization of the radiation.
Terahertz (THz) reflection spectroscopy has the potential to extract unique spectral signatures from various materials of interest, but these signatures can be distorted by rough surface scattering, low signal strength, and alignment errors. One method of addressing these challenges and increasing gain is to coherently combine information across frequency bands. This method, called correlation processing,...
We present a THz scattering-type scanning near-field optical microscope (THz s-SNOM) system. To estimate pure material resolution of our THz s-SNOM system, near-field images were obtained for embedded metallic grating. The pure material resolution of our THz s-SNOM system was estimated to be less than 100 nm.
We report on the method that terahertz generation and detection were simultaneously performed via non-collinear optical parametric interaction in a nonlinear crystals using a Si-photodiode. The bandwidth manipulation between broad 3.3 THz and narrow 45GHz bandwidths was demonstrated at single quasi-phase-matching crystal using the position-dependence of the crystal.
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