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A new method was used to predict the surface energies of three low-index surfaces for intermetallic compound B2-AgMg. The results show that Ag-terminal and Mg-terminal are the two kinds of surface models for (1 0 0) and (1 1 1) surfaces which are non-stoichiometry. (1 1 0) surface has only one surface terminal, which is stoichiometry, and the smallest surface energy (about 0. 8 6 2 J / m 2) in three low-index surfaces. The surface energies are related to the chemical potential of Ag and Mg atoms for (1 0 0) and (1 1 1) surfaces, but it is of no concern to this factor for stoichiometry (1 1 0) surface. Analysis of electronic properties is coincident with the calculated surface energies. [ABSTRACT FROM AUTHOR]

We consider a discrete model that describes a linear chain of particles coupled to two defects. This model can be regarded as a linear generalization of the familiar Fano-Anderson model. The analytical result for the plane wave transmission coefficient is obtained. Comparing the transmission coefficient of Gaussian wave with that of plane wave, we can draw a conclusion that arising perfect reflection due to destructive interference depends on the input waveform of incident particle and a necessary switching condition of Fano resonance is the input plane wave. This interesting feature may play a guiding role in devising various particle switches in theory and experiment. [ABSTRACT FROM AUTHOR]

The asymmetrical nested metamaterial, composed of two split-ring resonators (SRRs) and two embedded gallium arsenide (GaAs) islands placed in the two SRRs, has been elaborately designed on quartz substrate. Its tunable and switchable resonances at terahertz (THz) frequencies are numerically demonstrated here based on different conductivities of GaAs, which can be transformed from semiconductor to metallic state through appropriate optical excitation. Without photoexcitation, our designed metamaterial has three resonance peaks in the range of monitored frequency range, and they are located at 0.813, 1.269 and 1.722 THz, respectively. As the conductivity of the two GaAs islands increases, different new resonances appear and constantly strengthen. Finally, four new resonant points are generated, at 0.432, 0.948, 1.578 and 1.875 THz, respectively. At the same time, the metamaterial structure is changed from the original nested mode to a new integral mode. Applying reversible changing conductivity of semiconductor to push the conversion of resonance, this asymmetrical nested design provides a new instance in application and development of additional THz devices. [ABSTRACT FROM AUTHOR]

We demonstrate a method for obtaining optical coefficients over a broad terahertz spectral range from 1.5 THz to 16 THz at room temperature. Based on the interferograms directly acquired by a Fourier transform infrared spectrometer (FTIR), multi-beam interference principle combining Fresnel’s formula is employed to extract the refraction index and the extinction coefficient, giving the basis for calculating dielectric coefficients. It avoids the uncertainty and phase instability while using Kramers–Kronig (KK) relations and overcomes the limited frequency range of terahertz time-domain spectroscopy (TDS). Moreover, this method has better stability and is needless of cutting useful information between neighboring interference peaks for thin samples compared with TDS, making it a general processing method for interferograms and a good alternative for terahertz dielectric measurement. [ABSTRACT FROM AUTHOR]

We propose the design of a broadband planar metamaterial absorber (MA) at terahertz frequencies. The unit cell of the MA is composed of four dual-band sub-cells with different dimensions in a coplanar. The four dual-band sub-cell structures resonate at several neighboring frequencies. The absorber consists of two metallic layers separated by a dielectric spacer. Simulation results show that the metamaterial absorption at normal incidence is above 90% in the frequency of 6.56-8.10 THz. This design provides an effective way to construct broadband absorber. The multiple-reflection theory was used to explain the absorption mechanism of our investigated structures. The coupling of adjacent four dual-band sub-cells can introduce additional capacitance to affect the performance of absorber. [ABSTRACT FROM AUTHOR]

The characteristics of terahertz (THz) generation based on cascaded difference frequency generation (DFG) process in periodically inverted gallium arsenide () and gallium phosphide () is calculated from coupled wave equations, in which the output enhancement factors are 5.4 and 3.9 in the two crystals, respectively, compared with DFG without cascading. The optimal interaction length, influence of crystal absorption, wave vector mismatch and pump intensity are analyzed. A short discussion on wavelength tuning is also given. The calculated optimal operating parameters and conclusions can provide good directions for the experimental design. [ABSTRACT FROM AUTHOR]

We demonstrate a double-clad Nd3+-doped polarization maintaining fiber (PMF) amplifier at 1064 nm for a compact configuration of a high-gain and low-noise optical fiber amplifier. The proposed 125 μm inner-cladding diameter in the double-clad fiber provides the single-mode propagation of the signal lightwave into its doped core without misguiding the signal lightwave into the outer-cladding. The small signal gain of Nd3+-doped fiber amplifier is 24 dB, and its noise coefficient is less than 8 dB. [ABSTRACT FROM AUTHOR]