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The natural seraphinite has the optical phonon modes in the frequency range from 0.1 to 2 THz. The observed absorption modes at 0.8, 1.2, and 0.96 THz are understood as infrared active phonon modes of Au(z) and Bu(x, y) symmetries, respectively. The 0.96 THz mode is, in particular, strong and narrow comparable to the reported 0.53 THz mode in a-lactose monohydrate. Experiments carried out by THz time-domain...
A new approach to the design and the realization of a broadband multilayer anti-reflection (AR) coating is proposed in this study. The binominal multi-section transformer is employed to efficiently determine the thickness and the refractive index of each matching layer, while those layers can be further realized by doping different fraction of subwavelength-size silicon powders (for relatively-high-index...
We report a design of small-core, multiple-layer Bragg waveguide for guiding the terahertz (THz) signal using TE01 mode, which is composed of alternating high-index dielectric (HDPE) and low-index dielectric (air). The propagation loss is less than 0.1 dB per centimeter ranging from 0.95 THz to 1.20 THz, which is better than that of the traditional metallic tube. Furthermore, a novel scheme is proposed...
We obtain representations for static electric and magnetic fields induced by charged-particle current in a regular simply connected ideally conducting waveguide in the form of solutions to equations of the Kisunko-Vainshtein waveguide excitation theory.
Efficiency enhancement of electron devices with two concentric magnetically-confined annular charged-particle beams with the help of non-zero bias voltage applied to the inner conductor of a coaxial drift-tube is studied. The inner conductor bias voltage not greater than ±50 kV is capable of controlling the limiting currents of two electron beams on the level up to 15 %.
We suggest the new approach of sub-THz and THz signals generation based on intense electron beams containing oscillating virtual cathode. In this work we discuss the results of numerical simulation and optimization of the novel device called “nanovircator” that have been carried out. The results of the numerical study show the possibility of “nanovircator” operation at 0.1–0.4 THz frequency range.
We demonstrate experimentally a possibility of triple frequency multiplication in a simple CW clinotron (a BWO with inclined beam) oscillator. In the proof-of-principle experiment the device generated λb ≈ 2.8 mm (107 GHz) in the buncher section while in the catcher section 10 mW at λc ≈ 0.935 mm (321 GHz) were measured. The principal ability of a clinotron-type oscillator to pre-bunch a layer of...
We demonstrate THz pulses emitted by LTG GaAs large area interdigitated photoconductive antennas with frequency components from 0.3 to 20 THz. The THz radiation is characterized with a 20-μm thick ZnTe crystal and the dynamic range reaches 60 dB. Under an original optical excitation scheme, the emitted THz pulses show frequency-independent spherical wave front, which provides focusing of the THz beam...
The optical resonator of CAEP THz-FEL is optimized to ensure wavelength tunable in a wide range and high power operation. The FEL power strongly depends on the performance of the optical resonator including output efficiency, gain and round-trip loss. The optical resonator consists of metal-coated reflect mirror, the center-hole output mirror, waveguide. The influence of waveguide and Rayleigh length...
Terahertz technology has seen many advances over the past decades. Special interest for the use of this technology is directed to the detection of illegal drugs, explosives and other hazardous materials. These materials exhibit characteristic signatures at terahertz wavelengths which may be used to identify them. In this paper we present a method for detecting the presence of chemicals and other materials...
We study temperature dependence of terahertz dielectric properties of ferroelectric lead germanate crystal. Observed soft mode behavior directly indicates transition from displacement to order-disorder type of ferroelectric in the vicinity of phase transition point.
Photoluminesence(PL) and magneto-optics are classical routines to characterize electronic structures of semiconductors. We incorporated magnetic field with infrared (IR) PL based on a Fourier transform infrared spectrometer, such that thermal background disturbance is well eliminated and signal-to-noise ratio significantly improved. By resolving closely-spaced PL components in Hg1−xCdxTe at various...
GaSe1−xSx crystals were used for long-wave mid-IR generation by KTP OPO down-conversion. Optimal composition GaSe1−xSx, shown 6 times higher efficiency than that of GaSe. Significant structure strengthening was achieved with Al-doping.
The fabrication of low-cost metal-insulator-metal (MIM) diodes using a self-assembled monolayer as the insulating layer is presented. DC and AC analysis show that the diodes have excellent non-linear current voltage characteristics compared to those typically reported, with a zero-bias curvature coefficient ranging from 0.5 V−1 to 5.4 V−1, voltage responsivity of 1.9 kV/W at a frequency of 1 GHz....
In 2003, we demonstrated a non-destructive terahertz spectroscopic imaging of illicit drugs hidden in envelopes using a widely tunable THz-wave parametric source [1], though its dynamic range at that time was less than four orders. Recently, we have realized ten orders of dynamic range with an evolved injection seeded THz-wave spectrometer. Now we can detect drugs under much thicker obstacles than...
The nonlinear optical response of silicene in terahertz (THz) regime is theoretically studied. Since the intrinsic spin-orbit coupling gap of silicene is in the order of 1 THz, the optical response in few THz frequency regime is strongly enhanced by linear and nonlinear conductivity peaks. Furthermore, these conductivity peaks are gate-tunable. The frequency-tripling nonlinear optical current can...
We present the first absolute power measurement of a photoconductive terahertz (THz) emitter developed for time domain spectroscopy. The broadband THz radiation is generated by a high mobility InGaAs/InAlAs multilayer heterostructure photoconductive emitter packaged into a fiber-coupled housing. For detection a recently developed ultrathin pyroelectric thin-film detector with special conductive electrodes...
A beam characterization of a THz beam generated from the organic crystal DSTMS is presented. The simple, collinear phase-matching geometry for this crystal results in an M2 factor below 1.5, resulting in a focused field strength of more than 4 MV/cm.
The lack of high frequency source with a simple structure and enough power output at THz band limit the development of terahertz technology. As a result achieving high-power THz radiation has attracted many efforts. In this paper, we investigate the possibility of power synthesis at 0.11THz based on discrete sources. The simulation and test results show that with a precision digital phase control,...
We describe a new instrument, the Terahertz Limb Sounder (TLS) designed to measure upper atmospheric winds and temperature in the altitude regime between 100 and 150 km. It is based on Doppler measurements of the line of neutral atomic oxygen, OI, at 2.06 THz. This measurement takes advantage of a Schottky diode based all solid state receiver.
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