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Carrier dynamics in single-layered graphene has been studied by reflection-type of THz time domain spectroscopic ellipsometry (THz-TDSE) and optical-pump/THz-probe spectroscopy (OPTP). We successfully determined the frequency-dependent complex sheet conductivity of photo-excited monolayer Graphene from 0.3 to 16 THz. By analyzing with Drude model, the time dependence of Drude weight and carrier scattering...
In this paper we report electro-optic (EO) sampling of THz pulses using ferroelectric crystal in the non-collinear Cherenkov phase-matching scheme, where an effective velocity matching is achieved in an EO crystal with a large refractive index in the THz frequency region. We demonstrate efficient THz EO sampling using LiNbO3 and BaTiO3 crystals in the Cherenkov- phase-matching scheme. It is shown...
Careful investigation of the RF oscillation frequency generated by MW class long-pulse 140 GHz gyrotrons for the Wendelstein 7−X (W7-X) stellarator found discrete frequency hopping in steps of 5–10 MHz during the initial frequency down-tuning as well as in long-pulse “quasi” steady-state operation. The classical explanation for this behavior, such as electron beam acceleration voltage ripple and the...
In this paper, we review our recent progress on low dimensional room-temperature, high-gain, and broad-spectrum photodetectors based on InAs nanowires. Several novel infrared photodetectors based on InAs nanowire are fabricated showing a high photo-gain at room temperature.
The heart of the integrated antenna and detector is the matching network between them. In this paper, four type antennas for matching the small impedances of high temperature superconducting terahertz detectors at 650GHz are proposed. And the coupling efficiency has improved for high temperature superconducting YBa2Cu2Ox (YBCO) Josephson junction detector with these antennas. Meanwhile, the array...
In order to properly simulate cases in which gyrotrons exhibit fast temporally varying oscillations, such as non-stationary oscillations or possible dynamic After-Cavity Interaction (ACI), an adequate model for the beam-wave interaction has to be used. We will show that the commonly used assumption of considering a constant wave-field envelope during the electron transit time has to be abandoned....
A new type of a fully integrated vertical nanocontact THz photomixer was fabricated on LTG-GaAs/n+GaAs /SI-GaAs wafer with a single silver nanowire of 60nm. The new vertical structure provides simple fabrication steps and better performance in terms of stability and antenna integration. The THz output power itself can be increased due to high photocur-rent of ∼7.5mA and small device capacitance of...
Optical frequency up-conversion based on sum frequency generation is a promising technique for efficient single-photon detection because of commercially available detectors with high efficiency and low noise. We extended the frequency range of up-conversion detection based on sum frequency generation to far infrared at terahertz frequency using a periodically poled lithium niobate. Terahertz photon...
Theoretical and experimental investigations on the coaxial gyrotron with two electron beams has been carried out. The output power is measured with a calorimeter. The operating frequencies are measured with a detector and a frequency mixer simultaneously. The experimental results agree well with the theoretical predictions. The quasi-optical mode convertor for dual-frequency operation coaxial gyrotron...
Radiative losses of terahertz surface plasmons (SPs) on plane metal-dielectric interfaces have been studied. Experiments performed with “gold — zinc sulfate — air” plane structures at a 130 μm wavelength have shown that a thin-film dielectric coating of the metal of about λ/500 thickness could double the SP propagation length. In addition, an optimal dielectric layer thickness corresponding to the...
An adaptive focusing (AF) algorithm based on minimum-entropy (ME) method is proposed for THz single frequency holography to improve the depth of focus for practical image applications. Experiments in 0.2THz band were performed to confirm the effectiveness of the proposed algorithm.
In this paper, a low-voltage high-efficiency 330 GHz tunable gyrotron is investigated, which operates on the open-cavity TE6,2 mode and employs an electron beam with voltage of 20 kV, current of 0.5A, and pitch factor of 1.5. Simulation achieves a competitive efficiency, more than 40%, under the assumption of using copper circuit wall and electron beam of 5% velocity spread. Besides, the investigation...
The nature and formation of the glassy state still lack comprehensive understanding. In this work we present a careful terahertz, FTIR, far-infrared, low frequency Raman and computational analysis using density functional theory on the inter-molecular hydrogen bonding characteristics and how this changes above and below the glass transition temperature in amorphous sorbitol. We show that the changes...
We overview the results of experimental development of high-performance frequency filtering and beam focusing devices operating at subterahertz and terahertz frequencies. The quasi-optical band-pass and high-pass filters, as well as planar lenses implemented as subwavelength metallized microstructures with thickness both of the order and much smaller than the wavelength are described. The techniques...
Since their first demonstration in 2002, the development of terahertz frequency quantum cascade lasers has been extremely rapid. We overview some of the advances that have taken place and which have made the terahertz quantum cascade laser such a ubiquitous source. We also consider potential future directions for terahertz quantum cascade laser technology, including its use in satellite-borne instrumentation...
By using of high-resolution Terahertz time-domain spectroscopy, we show that both the fundamental and higher-order Mie resonances can be excited in both magnetic and electric modes with in the one-dimensional dielectric grating. Furthermore, their highly sensitive capability dependent on the frequency red-shift, line broadening, and transmission decreasing were investigated with increasing refractive...
With the application requirement and technology development, the necessity and tendency of Synthetic Aperture Radar (SAR) imaging within the framework of multidimensional space joint-observation, which are polarimetry, frequency, angle, time series and etc., evoke catholic interests in SAR imaging research nowadays. Recent research progress on the Multidimensional Space Joint-observation SAR (MSJosSAR)...
Terahertz (THz) conductivity of single walled carbon nanotube (SWNT)/poly-vinyl alcohol (PVA) composites has been studied in the frequency window of 0.3–2.0 THz. It is found that conductivity of these samples can be efficiently tuned by changing the length of the SWNTs and also the SWNT weight fraction. For the highest weight fraction at a frequency of 1 THz, longer SWNT sample (average length ∼ 15...
In this report, two mode converters are designed and fabricated to extract TE41 and TE01 modes for the generations of 0.4 THz and 1 THz signal by high-harmonic interaction with gyrating electron beam, respectively. The purities of the desired modes in these two converters are both higher than 90% with remarkably broad bandwidth (380 GHz to 420 GHz for TE41 mode and 910GHz to 995 GHz for TE01 mode)...
The Karlsruhe Institute of Technology (KIT) is working on a possible physical design of 2 MW coaxial-cavity gyrotrons for future fusion applications, initially considering a first demonstration fusion power plant (DEMO). One focus of the investigations is how successfully such gyrotrons can be operated at significantly different frequencies. The gyrotron design as presented here is optimized for operation...
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