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In this paper we used two dipole Ga-As antenna to generate and detect THz wave in time domain. In this setup we could generate pulses with 1ps duration time and frequency range between 100GHz and 3.5THz. Finally we added two confocal lenses to this arrangement and set up a THz-TDS system in transmission mode and we could identify a lactose sample by this arrangement.

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In this paper an imaging system based on the transmission modes in the terahertz (THz) region is developed by using a photoconductive antenna as source, and another photoconductive antenna as detector, and an oscilloscope and a Lock-in amplifier as data acquisition unit. The imaging of different objects in the composite box (wood and plastic) is tested at the THz band. The influence of object’s translation step on the THz imaging is discussed.

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The electromagnetic pulses in the terahertz spectral range (0.1-30 THz) have numerous applications in spectroscopy, biology and medicine, T-ray imaging and information technology. Therefore, in this paper, the THz generation due to the interaction of a femtosecond laser pulse and its second harmonic with a background gas is studied. In addition, the effects of the laser pulse initial phase, phase difference of the laser pulse and its second harmonic, the background gas type and its pressure on the generated THz field are investigated. The results show that the THz generation efficiency is increased with the increment of the background gas pressure and the decrement of its ionization potential. Moreover, increment of the pulse initial phase, and also the phase difference lead to the same result.

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In this paper the focus is on breast cancer detection and imaging methods and we want to present a method that has low photon energy radiations. In addition, the results present the high accuracy of this method in comparison with other methods. In this way, THz imaging plays an important role on giving detailed outputs very fast with low risk for patient. Also we do not need to stain the specimen for example in IHC or H & E methods. In this paper it is proved that with no damage and burn in T-ray imaging due to low temperature gain in breast tissue, by using the tissue absorption coefficients, various areas of adipose, fiber and tumor is distinguished in breast specimen. Then normal and cancerous borders in tissue will be recognized because normal tissue contains high amount of adipose and fiber. In addition, by using image processing methods the type of tissues are determined and the mean percentage of them are calculated.

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In this paper, the four-wave mixing in silicon waveguides is investigated for achieving suitable frequency range in the terahertz region. For this purpose, a silicon waveguide with appropriate dispersion properties is selected and by changing the input pump wavelength from the normal to the anomalous dispersion regimes around the vicinity of zero-dispersion wavelength, the generated terahertz radiation is tuned in a wide range. The results show that, via the change of the pump wavelength by 1.5 µm, a frequency shift from 38 to 309 THz can be obtained.
 

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In this paper, a bandpass filter is simulated using CST software. Considering that the width of the output spectrum of the filter is one of the most important factors in these types of filters, two of these filters are placed in intervals of wavelength, according to the principles of Fabry Perot, This will reduce the amount of bandwidth. This theory has been investigated in a range of frequencies (0.5 to 2.5 terahertz). Finally, the incidence wave angle on the filter has also been analyzed, which indicates that, depending on the angle of the incidence wave, the frequency peak of the output spectrum is displaced. Using this method, the output spectrum of the filter can be used in tunable applications.

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In this paper, the effect of temperature on THz radiation in superconductors media is investigated. Electromagnetic equations for vortices have been solved and the radiated power versus superconductors parameters is calculated. Results show that radiated power is slightly dependent on temperature for those much lower than critical temperature (T_c), but an effect of temperature is significant near T_c. The results also reveal that the peak of radiated power gets its maximum just before T_c and then decreases sharply.

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In this paper, a graphene-based plasmonic structure is proposed for simultaneous implementation of three-input logical XOR and XNOR operations. In this structure, the surface plasmon polaritons (SPPs) are stimulated at the interface of graphene and dielectric layers and their transmission are controlled by an external voltage source. In the presented logic gates, the input signals are electrical and the output signal is optical. Simulation results demonstrate that the extinction ratio (ER) of 10.33 dB is achievable for the designed gates. Also, the footprint of the proposed structure is less than 1.5 μm². Our studies have shown that a structure for simultaneous three-input logical XOR and XNOR operations has not been reported so far.

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In this research, Terahertz Time Domain Spectroscopy (THz-TDS) system in reflection 30 degree mode has been established for detection of  RDX. In this setup, two gallium arsenide photoconductive antennas have been used to generate and detect the terahertz pulses with frequency range between 0.1 and 2 THz. By using of data detection, absorbtion and refraction coefficient are calculated 1.5 and 108.7. That data good agree with reference.

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In this research, have been used THz Time Domain Spectroscopy(THz-TDS) at reflection mode contain two dipole GaAs photoconductive antenna in order to generation and detection THz waves and optical instruments such as silicon lens and parabolic mirror. generated Terahertz pulses have subpicosecond pulse duration  and spectral range of 0.1-2 THz. Absorption and refractive coefficients of histidine were calculated about 45.2 cm^-1 and 1.57 respectively. Ability of concealed  samples detection is one of the advantages of this method.

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In this paper, a wideband Vivaldi antenna is designed for the frequency range of 0.5-3 THz and simulated by a software package based on the finite element method.  The antenna has dimensions of 432µm × 400µm ×10.2µm, its substrate is quartz, and the conducting layers are made of gold. The designed antenna is highly directive; its directivity in the above mentioned frequency range is between the minimum of 4.53 dB and the maximum of 9.40 dB. Also, from simulation results, its maximum gain and efficiency were found to be 8.50 dB and 84.43%, respectively which make it superior to similar antennas reported in the literature.  The proposed antenna can be used in THz imaging and spectroscopy to detect materials that have THz signatures in this region.

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In this paper, generation of terahertz (THz) radiation by the beating of two super- Gaussian laser beams in a nanocluster plasma is investigated, theoretically. The electric field of laser beams interact with the nanocluster, leads to the ionization of the cluster atoms, and producing nanoplasma. Interaction of laser beams with the electronic clouds of nanoplasma generates ponderomotive force that leads to the creation of a macroscopic electron current at the beat frequency which can generate THz radiation. The THz wave equations and THz efficiency are analytically derived in nanocluster plasma medium. The effects of the density and radius of nanoclusters, the laser beam width and intensity of super- Gaussian lasers on the THz radiation efficiency has been investigated in a nanoplasma- based THz emitter. The results indicated the maximum value of the field amplitude for THz radiation is the near the frequency of  f~13.57 THz, that is, when the beat- wave frequency approaches the effective plasmon frequencies of the nanoplasma.
 

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By investigating nonlinear optical parameters of some conventional second order nonlinear materials, the nonlinear process of difference frequency generation at terahertz frequency range is simulated in waveguides made of these materials with the same geometry. In order to compare the results obtained in these waveguides, we have employed a figure of merit, based on the ability of the structure to convert input frequencies to terahertz frequency. The comparative results are presented for ZnO, GaAs, InP, and InP.

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THz radiation has various applications from medical to security. However, sensitive detection of THz radiation at room temperature has complications. Graphene due to fast charge carrier dynamics is an ideal material for different applications like photodetection. Because of constant 2.3% absorption of graphene in a wide range of frequencies, increasing graphene absorption is necessary for any application. Plasmonic effects in graphene-metal interfaces can be used to solve this problem; which can improve graphene absorption in resonance frequency even to 80% with increasing electric field magnitude. Photo-thermoelectric (PTE) effect is an inspiring detection mechanism in graphene. Photo-excited carriers thermalize rapidly due to strong electron-electron interactions and low electronic heat capacity of graphene. In this article a graphene based photo-detector in THz range have been designed and simulated benefiting photo-thermoelectric effect.

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In this paper, a regenerative terahertz parametric amplifier with a high tuning range based on the four-wave mixing process in TOPAS is investigated. A terahertz wave seed with a peak power of 2W, under optical pumping with suitable pulse length, peak power and wavelength, can produce amplified terahertz with a central frequency in the range of 4.7 to 14.6 THz. The results of the optimal state show that the gain of amplification for one round trip inside the cavity and in the best phase matching conditions, at a frequency of 9.6 THz is equal to 1.049, which leads to the production of a terahertz wave with a maximum power of 2.098 W.