Traveling wave solutions for two nonlinear evolution equations with nonlinear terms of any order

In this paper, based on the known first integral method and the Riccati sub-ordinary differential equation (ODE) method, we try to seek the exact solutions of the general Gardner equation and the general Benjamin-Bona-Mahoney equation. As a result, some traveling wave solutions for the two nonlinear equations are established successfully. Also we make a comparison between the two methods. It turns out that the Riccati sub-ODE method is more effective than the first integral method in handling the proposed problems, and more general solutions are constructed by the Riccati sub-ODE method.     

真空中两个点电荷间电势为零的点及其产生的场强

以真空中的两个点电荷为研究对象,讨论了空间坐标系下电势为零的点所形成的轨迹,以及电势为零的点的场强大小及方向;并通过MATLAB进行数值模拟,验证了结论的正确.总结了空间场强求解的一般方法和要点,明确了场强的空间分布性.     

Image displacement based on phase-encoded reference joint fractional transform correlator

In order to utilize the space of an input plane efficiently and make the optical structure more flexible, an image displacement measurement based on phase-encoded reference joint fractional transform correlator (PER-JFrTC) is proposed. We use a random phase mask to encode the reference image and overlay it with the target image forming the input image. Joint power spectrum (JPS) of the input image is obtained by Fourier transform and the resultant is encoded by the same phase mask. Then a fractional Fourier transform with an order p is applied to the phase-encoded JPS (PJPS), resulting in a correlation output with a sharp cross-correlation peak, which includes the displacement information between the reference and the target image. Contrast to displacement measurement based on traditional joint transform correlator (JTC), PER-JFrTC can use the space of the input plane efficiently and reduces the influence of the auto-correlation. Also the position of cross-correlation peak can be fixed arbitrarily according to the fractional order p as well as the optical set-up can be more flexible and easier to implement. Results based on digital computation show that PER-JFrTC could detect the displacement accurately and verify our proposal. A possible optical set-up is suggested.     

Analysis on dependence of phase matching angle on temperature in KDP crystal

The dependence of the phase matching (PM) angle on temperature in type-I second harmonic generation (SHG) and type-II third harmonic generation (THG) of KDP is experimentally investigated. The experimental results show that as the crystal temperatures vary by 1 °C, the external PM angles of the KDP doubler and tripler change 100 μrad and 220 μrad, respectively. The PM angle of KDP tripler is more sensitive to temperature variation than is that of the KDP doubler. Comparing the numerical calculations and the previous reports, a discrepancy has been found among the different reported results. Based on the analytical solution of the temperature dependence of the SHG process it is shown that a small error in the thermo-optic coefficients of the crystal is the main factor source of the discrepancy.     

Microstructure, optical and static recording properties of AgOx film, and near-field simulation of sub-wavelength aperture based on the AgOx marks’ formation

Structures, spectra and surface topographies of as-deposited and annealed AgO_x films have been investigated by an X-ray diffractometer, a spectrophotometer and an atomic force microscopy (AFM). X-ray diffraction and spectrum results show that the as-deposited AgO_x films with high oxygen ratios (x≥0.5) are in amorphous states and Ag crystalline particles will separate out after annealed. AFM results show that the film surface will become much rougher and film thickness will increase greatly after annealed due to the decomposition of AgO_x with release of oxygen. Static recording results show that two microstructures of the recording marks can be produced: one is the bubble mark at a low recording power and the other is the rupture bubble with an ablated aperture (hole) in the center at a high recording power. Based on the formation of rupture bubble marks, the near-field optical distribution of a focused Gaussian laser beam through a sub-wavelength aperture (200 nm in diameter) has been simulated using finite-difference-time-domain (FDTD) method. Results show that the spot size can be greatly squeezed with still highly transmitted intensity, which may lead to the super-resolution readout.     

An efficient scheme for preparation of multipartite entanglement of atomic ensembles

We propose an efficient scheme to prepare multipartite entanglement of atomic ensembles trapped in separate cavities. Our scheme has high fidelity even with realistic noise based on the repeat-until-success strategy. By employing the quantum memory of the atomic internal state, the scaling efficiency decreases only with the number of atomic ensembles by a slow polynomial law. Moreover, the atomic ensembles also can function as quantum repeaters, which enable our system to compatible with the current experimental technique for quantum communication using atomic ensembles.     

A novel method for measuring optical fiber delay lines based on the optical fiber low-coherence Young's interferometer

According to the principle of double-beam interference imaging using an infrared broadband light source, a novel method based on the optical fiber low-coherence Young's interferometer for the measurement of programmable optical fiber delay line is proposed. By measuring the small length increments of delay fiber through the evaluation of the central positions of zero-order interference fringes, we successfully construct a system with a variety of important functions, such as real-time controlling, measurement and displaying. This system offers the benefit that it can be regulated precisely to generate interference stripes once again after the length of fiber segment changes. When the locations of central stripes are moved to coincide with the original markers, the determination of the corresponding fiber optical delay time becomes really simplified, as just by reading out the tinny displacement of the reference arm. Multiple groups of experimental results demonstrate the outstanding performance of the proposed system since it bears a measuring accuracy of μm and a measuring range from 1 mm to 20 cm.     

The system design and assemble for the high resolution telescope system with segmented aperture

A design method along with its results, for a space optical system with high resolution and wide field of view, is described. Such optical systems can be used in the infrared as well as visible configurations. The proposed design is based on an on-axis Ritchey-Chrétien system with corrected lens element while the primary mirror is a segmented aperture. Here the on-axis concept allows wide-field enabling a variety of observations designed for the multi-object spectrometer instruments, optimized for low scattering and low emission of light. The use of segmented mirrors in the optical system allows adopting any method for its fabrication purposes. Segment results are discussed and the image quality of the design based on these results is evaluated in this paper.     

The role of surface terminations on the band structure and optical properties of silicon nanonets

The ab initio calculations are carried out to investigate the effect of hydrogen, oxygen and nitrogen terminations on the properties of the band edge and the values of the band-gap, as well as the oscillator strength of the silicon nanonets (SiNNs). The oxygen functional groups are found to effectively preserve the direct band-gap nature of the SiNNs, and even change the luminescence properties of the silicon nanowires (SiNWs) to the direct band-gap transition. The appreciable oscillator strength of the first direct transition is obtained for the oxygen terminated nanostructure. The study on the electronic states indicates that the variation of the band edge caused by the surface terminations is attributed to the change of the state compositions. These surface modifications are thought to be useful for silicon band-gap engineering in the area of optoelectronics.     

Preparation and properties of SnS film grown by two-stage process

SnS films have been prepared by a novel two-stage process. It involved sputtering of Sn film on glass substrate and sulfurization of the thin metallic tin precursor layers in a vacuum furnace. The X-ray diffraction results showed that the SnS layers had orthorhombic structure and (0 4 0) preferential growth is more and more obvious with the increase of sulfurization time. The SnS film obtained by this work shows high optical absorption efficiency, and the film has a direct optical band gap of about 1.3 eV. The films show p-type conductivity and the resistivity of SnS film decreased obviously under illumination.