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We have explored the low-energy dynamics in the half-doped Eu0.5Sr0.5MnO3 using terahertz time domain (TDS) spectroscopy. Observation of a finite frequency peak structure in optical conductivity at around ∼4meV suggests low-energy excitation, presumably the charge-density waves.
The terahertz time-domain spectroscopy (THz-TDS) technique has recently been in progress with a wide range of research and industrial applications. A precursory THz-TDS instrument has been newly developed for application to pharmaceutical process analytical techniques (PAT). An overview of the newly developed instrument performances and one of the latest applications will be described in focus on...
Nanoscale materials have some unique properties in THz band. Preliminary measurement has been conducted using a quasi-optical (QO) bench to explore the transmission characterization of Gold Nanoparticle (GNP) suspensions over the W-band (75–110 GHz).
Isothermal crystallization of poly(3-hydroxy-butyrate) was studied by terahertz time-domain spectroscopy. The temporal change of the ratio between the crystalline and amorphous structure was estimated by the integrated absorption intensity. The crystallization process was discussed by using Avrmi's equation.
A time resolved study of the THz plasmon dynamics in a random metallic ensemble is presented. This investigation is performed via a THz pump-THz probe experiment. It is illustrated that the electric field of the transmitted THz probe pulse shows an enhancement when the metallic ensemble is first excited by means of a THZ pump pulse. The effect is studied versus the temporal delay of the probe pulse...
In order to study on THz radiation pick upping by use of graphene nano-structures, we explore the use of quntum dot as nano scale GHz-THz detector with a high sensitive and/or a wide range frequency response. A fundamental possibility in the device application has been studied.
In a tomographic imaging system, the key is to collect a sufficient number of scattered field points to recover the currents in the inverse scattering problem. This can be accomplished by using a real array of multiplexed antennas for real time imaging. In this paper, a W-Band Retina for Terahertz tomographic imaging is presented. A system based on a retina, a collector and an illuminator is described...
We measured the properties of human skin using THz techniques: 1) THz tomography with a high depth resolution; 2) stratum corneum measurements using a metallic-mesh sensor or interference THz sensing; and 3) a possible sweat duct helical antenna in the THz region. We also studied the non-thermal effect of THz/MMW radiation on human skin cells.
We fabricated GaAs air-bridge Schottky diodes and pseudomorphic InGaAs/AlGaAs heterostructure field-effect transistors with similar on-chip lithographic antennas. Detectors were packaged with a silicon lens and their rectified signal when exposed to 450–700 GHz radiation was compared.
As part of a study for a second generation heterodyne spectrometer on SOFIA we are developing a 2.5-THz frontend which is implemented in a pulse-tube cooler. It consists of a quantum-cascade laser as local oscillator and a phonon-cooled NbN hot electron bolometric mixer. Frequency stabilization to below 300 kHz full width at half maximum is achieved by locking to a molecular absorption line. We will...
The direct transition from o-Ps to p-Ps was firstly observed, using a gyrotron, a mode-converter and a Fabry-Pérot cavity. The Einstein's A coefficient is measured as 3.9 (+1.8 −1.7) • 10−8 s−1. It is the first step to directly examine a reported discrepancy of positronium hyperfine splitting.
The nonstationary spectrometer of 500–700 GHz frequency range is presented. Radiation sources are harmonics obtained by semiconductor superlattice frequency multiplier. The receiving system is developed using a superconducting integrated receiver. The results of test measurements of NH3 absorption lines (572 GHz) in exhaled air were presented.
An efficient terahertz (THz) wave generation via Cherenkov-type phase matching has been demonstrated using a thin lithium niobate (LiNbO3, LN) crystal coupled to a Si prism structure (Si-LN). This design relies on wave-guiding effects for the optical pump and decreased THz absorption in the LN crystal to achieve intense THz wave emission. In addition, an efficient THz electro-optic (EO) sampling has...
This paper describes a passive terahertz wave imaging system employing an opto-mechanical scanner. The terahertz images of a person acquired in reflection and transmission geometries are presented. Results show the systems are promising for real security applications.
We present the results of our studies of the possibility of developing a heterodyne receiver incorporating a hot-electron bolometer mixer as the detector and a semiconductor superlattice multiplier driven by a reference synthesizer as the local oscillator. We observe that such a local oscillator offers enough power in the terahertz range to pump the HEB into the operating state.
The SELFT code has been modified to study the influence of B=B(z) on spurious oscillations. An initial attempt has been made to simulate the spurious oscillations in the cavity for an example (W7X 140GHz, TE−28, 8 mode gyrotron). The radio frequency (RF) spectrum at the end of the simulation (using B=B(z)) clearly indicates the presence of spurious oscillations.
A sub-terahertz gyrotron is designed to be used as a radiation source of an active real-time imaging system for food safety inspection. The gyrotron employed with compact cryogen-free magnet, is expected to produce 10 W-level in continuous wave at 408 GHz. Details of the gyrotron design as well as the concept and configuration for the real-time imaging system will be discussed.
Sintered tungsten wire, reservoir cathodes offer high current density operation with very long life time and extremely uniform emission current. The cathodes, however, should be designed for the specific performance requirements of the device. This presentation provides information on performance capabilities and describes the design process
Spectroscopic terahertz imaging with the InGaAs-based bow-tie diode as room temperature THz detector was proposed. Images were recorded in transmission mode from 0.5 THz up to 2.5 THz applying an optically-pumped molecular THz laser. The content of compounds in test samples was studied and discriminated from the spectroscopic imaging results along with Fourier spectroscopy data.
We report a distributed tapered sever design for a 220 GHz sheet beam TWTA circuit, compatible with MEMS precision micro-fabrication process. The loss material (Si/SiC) is introduced gradually into the cavities of the double-vane half period staggered structure of the TWTA starting from a thickness of 10 μm and gradually increased in successive cavities to a maximum value (less than 270 μm which is...
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