On the Volume of Unit Tangent Spheres in a Pinsler Manifold

Motivated by some issues which enter into the Gauss-Bonnet-Chern theorem in Finsler geometry, this paper studies the unit tangent sphere (or indicatrix) I_x M at each point x of a Pinsler manifold M. We demonstrate that the volume of I_mM, calculated with respect to a Riemannian metric induced naturally by the Finsler structure, is in general a function of x. This contrasts sharply with the situation in Riemannian geometry. We also express the derivative of such volume function in terms of the second curvature tensor of the Chern connection. In particular, we find that this function is constant on Landsberg spaces (though that constant need not be equal to the value taken by Riemannian manifolds).     

Electron entanglement detected by quantum spin Hall systems

We propose a promising electron entanglement detector consisting of two quantum spin Hall systems weakly coupled to a superconductor. The detection of electron spins along various polarization directions, which is a prerequisite for testing Bell's inequality on solid state spins, can be achieved in an all-electrical-controlled manner utilizing the helical edge states. It is found that the violation of Bell's inequality exists in a large range of the tunneling parameters, which can be realized in mercury telluride quantum wells.     

Non-specular reflection of self-collimated beams in photonic-crystal-made prism and waveguide system

We demonstrate a dual-beam-reflection phenomenon for a Gaussian beam illuminating at a Kretschmann configuration composed of a photonic-crystal-made prism and a dielectric waveguide. One reflection beam has a positive shift and the other has a negative shift. The finite-difference time-domain (FDTD) shows that the specific phenomenon takes place only when the corresponding quasi-guided mode supported in the Kretschmann configuration is excited. Field profile of the quasi-guided mode demonstrates a strong localized stationary field in the dielectric waveguide. We found that the maximum positive lateral shift (LS) is 14.27a (where a is the lattice constant), corresponding to 3.07 times of the incident wavelength, which is 0.7135 times of the beam waist and much larger than that in some previous reports.     

Optimization of two-photon absorption enhancement in one-dimensional photonic crystals with defect states

One-dimensional photonic crystals with a defect layer of CdS were fabricated. The observed enhancement of two-photon absorption (TPA) in the CdS layer can be attributed to the intensified optical field confined within the defect layer of the photonic crystal. The results show that the enhancement of TPA coefficient depends basically on the number of periods of the photonic crystal and the defect mode position in the photonic band gap. The observation agrees qualitatively with the expectations of a computation by matrix transfer formulation.     

激光导致水击穿和等离子体形成过程的物理分析

对短脉冲激光作用水介质中引起光学击穿的机制进行了分析,通过自由电子密度速率方程的数值解确定激光的击穿阈值.将数值计算结果与波长在可见光和近红外波段,脉宽为ns、ps和fs的激光脉冲在纯净水和含有杂质的水中的实验测量的击穿阈值作了比较.还计算了等离子体中自由电子密度的演化、等离子体吸收系数和能量密度.通过解自由电子密度速率方程得到结果与实验测量的值符合得很好.     

Focusing of helico-conical cosh-Gaussian beam

Helico-conical beam is attractive for its phase front is nonseparable helical and conical phase function, which produces a spiral intensity distribution occurs at the focal plane. In this letter, the focal properties of cosh-Gaussian beam with helico-conical wavefront were investigated to show that helico-conical phase front does not always produce spiral intensity distribution. On increasing decentered parameters in cosh parts of the beams, the spiral focal pattern evolves into multiple intensity peaks with center main strongest peak. Under condition of higher decentered parameters, the focal spiral curve disappears. In addition, the topological charge also affects the focal pattern considerably.     

Interfacial differences in enhanced schottky barrier height Au/n-GaAs diodes deposited at 77 K

The use of cryogenic temperatures (∼77 K) during Au Schottky contact deposition onto n-GaAs produces an increase in barrier height from 0.73 eV for room temperature diodes to 0.82 eV. Not all Schottky metals show this enhancement—for example Pt and Ti do not show any significant change in barrier height whereas Au, Pd and Ni show increases between 7 and 18%. We used X-ray reflectivity to show that the main difference between Au deposited at 77 K and room temperature is a decreased metal roughness while the interfacial roughness between the Au and GaAs is basically the same. As the diodes are annealed to 300 °C both the difference in barrier height and interfacial roughness is lost. This is a simple method with potential for improving the performance of GaAs metal-semiconductor-field-effect-transistors (MESFETs).     

The computation of axisymmetric, supersonic nozzle arc usingadaptive grids

The computational difficulties associated with an arc burning in an axisymmetric supersonic nozzle are mainly caused by the region (known as the boundary) surrounding the are core within which temperature changes rapidly. When the arcing current decreases, this boundary collapses rapidly towards the axis. An adaptive grid scheme based on the temperature gradient is used to solve the dynamic are conservation equations in the computational domain. A direct grid adaptive scheme relates the solution in the computational domain to that in the physical domain without interpolation. Numerical results are compared with the experimental results as well as other numerical solutions obtained respectively by using a uniformly distributed, fixed grid system in the physical domain and by the solution adjusted method. A good agreement is achieved