Based on a master oscillator power amplifier configuration, laser performance of commercial Nufern-20/400-8M Ybdoped aluminophosphosilicate ternary laser fiber was investigated. Pumped by 976 nm laser diodes, 982 W laser output power was obtained with a slope efficiency of 84.9%. Spectrum of output was centered at 1066.56nm with 3dB bandwidth less than 0.32 nm, and the nonlinearity suppression ratio was more than 39dB. Beam quality of Mx2 and M2y were 1.55 and 1.75 at 982 W, respectively. The laser performance indicated that Nufern-20/400-8M Yb-doped aluminophosphosilicate ternary laser fiber is highly competitive for industry fiber laser use.
A first principles study has been performed to systematically evaluate the mechanical properties and stabilities of pristine, hydrogenated and fluorinated silicene (H-silicane and F-silicane) under tension. The uniaxial tension along the armchair (AC) and zigzag (ZZ) directions and the equiaxial tensile strain are considered in this work. The calculated results have shown that the deformation, failure behavior and the ideal strength are anisotropic along the three deformed directions. After hydrogenation and fluorination, the ideal strengths in three deformed directions all reduce while the ideal strains increase. Therefore, the hydrogenation and fluorination increase the toughness. The phonon calculations based on the density functional perturbation theory (DFPT) confirm stabilities of the pristine silicene, H- and F-silicane. The Poisson ratios of three materials along the AC and ZZ directions all exhibit monotone decreasing changes with increasing strain, except that the Poisson ratio of pristine silicene in the zigzag direction increases with increasing strain. The tensile strains decrease the buckling height, as expected, but in a complex function. The second- and third-order elastic constants are determined by least-squares polynomial fitting to the first principles calculations. Our results can help to understand the effect of hydrogenation and fluorination of silicene on its mechanical properties and provide some useful data for the experiments.
A general model in satellite-to-ground quantum communication is proposed by investigating the effect of a laser acquisition, pointing, and tracking (APT) system on the polarization state of single photons. The eccentricity of the general model ranges from 0 to 1, which means that a circular orbit can be introduced reasonably. Moreover, the geocentric-equatorial coordinate system, which can utilize the two-line elements, is used in the general model. Two kinds of simulations are performed, and we found that the rotations of polarization state are obviously influenced by the APT system. Our model could be applied in a realistic satellite-to-ground quantum communication system.
Off-plane band structure for triangular and square lattice with non-zero kz component were calculated using Plane Wave
Expansion Method. Both decreasing, finally breaking down of in-plane band gaps and emerging of new off-plane band
gaps were observed with an increasing kz. Kz component dependence of band gap was investigated in both triangular
and square lattice, with varied air hole radius and dielectric constant.
A first-principles study has been performed to evaluate the electronic and magnetic properties of the Zn1-xMnxO1-yNy
system. Doping Mn atoms introduces local magnetic moments, while doping N atoms introduces carriers. It is worth
noting that intrinsic Mn-doped ZnO favors antiferromagnetic (AFM) ordering, and this cannot be changed by raising Mn
ions concentration continuously. However, by the codoping N and Mn, it is possible to change the ground state from
no-metallic AFM to half-metallic ferromagnetic (FM) and make ZnO as a dilute magnetic semiconductor. We have
succeeded in describing the change (from AFM to FM) by using the magnetic interaction that is hole-mediated FM due to
the hybridization between N 2p and Mn 3d states. Furthermore, the most stable configurations are found to be
-O-Mn-N-Mn-O-.Our results are in good agreement with other theoretical results that are additional holes carriers is one
of the possible mechanisms.
Molecular dynamics simulations using the Tersoff potential have been performed to investigate the perturbation effects
caused by different kinds of the point defects (vacancies and substitutional impurities) on the strained and relaxed Si
matrices. Lattice distortion, mean square displacement, pair correlation function and vibrational spectra are studied. It is
found that Ge substitution lead to little distortion of the Si matrix. However, vacancy and C substitution lead to more
distortion. Diffusion directions of Si atoms around different kinds of point defects are different. When C substitution is
introduced in the relaxed Si matrices or Ge substitution is introduced in the strained Si matrices, the system needs longer
time to reach equilibrium. The crystallinity and symmetry degree of relaxed Si matrices are more satisfying than those of
strained Si matrices after relaxation. Changes of the vibrational spectra caused by vacancy and C substitution are obvious.
All above have a great effect on the photoelectric properties of the materials.
The work in this paper is based on a powerful function-fmincon in matlab and Finite Element Method, optimizing the
shape and the position of dielectric rods surrounding the termination of a photonic crystal waveguide, in order to increase
the directional emission. The method is simple, but can lead to useful results efficiently. More than fivefold improvement
in power incident upon a target area over a simple termination is achieved, and the optimized structure is easier for