Abstract: The dipole mode in triangular photonic crystal single defect cavity is degenerate. By deforming the lattice in photonic crystal we can obtain non-degenerate dipole modes. Lattice deforming in the whole photonic crystal destroys the characteristic of symmetry, so the distribution of the electromagnetic field is affected and the polarization of the electromagnetic field is also changed. Lattice deforming divides the degenerate dipole mode into the x-dipole mode and the y-dipole mode. It is found that the non-degenerate modes have better properties of polarization. So the high polarization and single dipole mode photonic crystal laser can be achieved by deforming the lattice of photonic crystal. In this paper, we simulated the cavity in photonic crystal slab and mainly calculated the quality factor of x-dipole mode under different deforming conditions and with different filling factors. The properties of polarization of x-dipole and y-dipole modes are also calculated. It is found that the ratio of intensities of Ex to Ey in x-dipole mode and that of Ey to Ex in y-dipole mode are 44 and 27, respectively.

Abstract: The magnetic plasmon (MP) modes in metal-dielectric-metal nanosandwich structures are investigated numerically using finite-difference time-domain method. We demonstrate the law of the quality factor in this kind of resonator.According to the MP modes in the nanosandwich structures, we design a series of resonators of this kind in order to investigate how to tune the resonante frequencies of MP modes through tuning the geometrical parameters and the dielectric layer refractive index of resonators, and the obtained result is well consonant with our analysis by the equivalent inductance capacitance circuit. We also investigate the electromagnetic energy confinement of the nanosandwich resonators, and analyse the Q factors of these structures from thermal and radiant points of view, which will guide one in designing new waveguides and lasers based on MP modes.

Abstract: We present the research on the transmission characteristic of slow-light-mode in the photonic crystal line-defect waveguide bends on SOI. After optimizing the structure parameters in the vicinity of the bends, the normalized transmission efficiency of slow-light-mode through the photonic crystal 60 degree and 120 degree waveguide bends are as high as 80% and 60% respectively, which are 10 times higher than that in the undeformed case. To slow down light further, we design novel coupled cavity waveguide bend structures with high qulity-factor. High normalized transmission efficiency of 75% and low group velocity of c/170 (c is the light velocity in vacuum) are realized. These results are beneficial to enhance the slow light effect of photonic crystal structures and improve the miniaturization and integration of photonic crystal slow light devices.

Abstract: Inspired by the idea of the stero-coupling, we propose a new sandwich-like photonic crystal microcavity which is composed of double layer photonic crystal slabs H1 (DLPCS-H1) cavity with an air layer in between. We calculate the electromagnetic field distribution and the quality factor of the dipole mode by the three-dimensional finite-difference time-domain method and the Padé approximation method. Through carefully analyzing the effect of the air layer height on the quality factor of the dipole mode, we obtain an optimized DLPCS-H1 cavity in which the height of intermediate air layer is about 0.5a (a is the lattice constant, a=420 nm). In this cavity, the quality factor of the dipole mode is 4 times as large as that of the conventional single layer photonic crystal slab H1 cavity. Furthermore, we study the three-layer photonic crystal slabs H1 cavity, and the quality factor of its dipole mode is increased over 7 times.

Abstract: The control of the photonic crystal waveguide over the beam profile of vertical-cavity surface-emitting lasers is investigated. The symmetric slab waveguide model is adopted to analyze the control parameters of the beam profile in the photonic-crystal vertical-cavity surface-emitting laser （PC-VCSEL）. The filling factor （the ratio of the hole diameter to the lattice constant） and the etching depth control the divergence angle of the PC-VCSEL, and the low filling factor and the shallow etching depth are beneficial to achieve the low-divergence-angle beam. Two types of PC-VCSELs with different filling factors and etching depths are designed and fabricated. The experimental results show that the device with a lower filling factor and a shallower etching depth has a lower divergence angle, which agrees well with the theoretical predictions.

Abstract: As a major component in the air, nitrogen emits fluorescence when it interacts with intensive laser field. The fluorescence comes from the first negative band system (〈inline-formula〉〈tex-math id="M7"〉\begin{document}${{\rm{B}}^{{2}}}\Sigma _{\rm{u}}^{{ + }} \to {{\rm{X}}^{{2}}}\Sigma _{\rm{g}}^{{ + }}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M7.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M7.png"/〉〈/alternatives〉〈/inline-formula〉 transition) of 〈inline-formula〉〈tex-math id="M8"〉\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M8.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M8.png"/〉〈/alternatives〉〈/inline-formula〉 and the second positive band system (〈inline-formula〉〈tex-math id="M9"〉\begin{document}${{\rm{C}}^{{3}}}\Pi _{\rm{u}}^{{ + }} \to {{\rm{B}}^{{3}}}\Pi _{\rm{g}}^{{ + }}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M9.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M9.png"/〉〈/alternatives〉〈/inline-formula〉 transition) of 〈inline-formula〉〈tex-math id="M10"〉\begin{document}${{\rm{N}}_{{2}}}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M10.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M10.png"/〉〈/alternatives〉〈/inline-formula〉. Under the action of high-intensity femtosecond laser, 〈inline-formula〉〈tex-math id="M11"〉\begin{document}${{\rm{N}}_{{2}}}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M11.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M11.png"/〉〈/alternatives〉〈/inline-formula〉 can be directly photo-ionized into 〈inline-formula〉〈tex-math id="M12"〉\begin{document}${\rm{N}}_{{2}}^{{ + }}{{(}}{{\rm{B}}^{{2}}}\Sigma _{\rm{u}}^{{ + }})$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M12.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M12.png"/〉〈/alternatives〉〈/inline-formula〉, which results in fluorescence emission of 〈inline-formula〉〈tex-math id="M13"〉\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M13.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M13.png"/〉〈/alternatives〉〈/inline-formula〉. In the process of femtosecond laser filament formation, the dynamic processes such as ionization and excitation of nitrogen molecules are affected by the laser intensity distribution and laser polarization direction. The products show different distributions in the propagation direction and radial space, which, in turn, affects its light emission. Therefore, it is necessary to further ascertain its generation mechanism through the spatial distribution of nitrogen fluorescence. In this experiment, the spatial distribution of the nitrogen fluorescence emission generated by linearly polarized femtosecond laser pulse filaments in air is measured. By changing the polarization direction of the laser to study the distribution of nitrogen fluorescence in the radial plane, it is found that the fluorescence emission of 〈inline-formula〉〈tex-math id="M14"〉\begin{document}${\rm{N}}_2^ + $\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M14.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M14.png"/〉〈/alternatives〉〈/inline-formula〉 is more intense in the direction perpendicular to the laser polarization, while it is weaker in the direction parallel to the laser polarization. The nitrogen fluorescence emission has the same intensity in all directions. The ionization probability of a linear molecule depends on the angle between the laser polarization direction and the molecular axis, which is maximum (minimum) when the angle is 〈inline-formula〉〈tex-math id="M15"〉\begin{document}${{{0}}^{\rm{o}}}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M15.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M15.png"/〉〈/alternatives〉〈/inline-formula〉(〈inline-formula〉〈tex-math id="M16"〉\begin{document}${{9}}{{{0}}^{\rm{o}}}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M16.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M16.png"/〉〈/alternatives〉〈/inline-formula〉). The 〈inline-formula〉〈tex-math id="M17"〉\begin{document}${{\rm{N}}_{{2}}}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M17.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M17.png"/〉〈/alternatives〉〈/inline-formula〉 gas is more likely to be ionized in the laser polarization direction, the nitrogen molecular ions 〈inline-formula〉〈tex-math id="M18"〉\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M18.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M18.png"/〉〈/alternatives〉〈/inline-formula〉 and electrons are separated in the direction parallel to the laser polarization. Therefore, more ions (〈inline-formula〉〈tex-math id="M19"〉\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M19.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M19.png"/〉〈/alternatives〉〈/inline-formula〉) are generated in the direction parallel to the laser polarization, and the fluorescence emission of 〈inline-formula〉〈tex-math id="M20"〉\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M20.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M20.png"/〉〈/alternatives〉〈/inline-formula〉 is more intense. Along the propagation direction of the laser, it is found that the fluorescence of 〈inline-formula〉〈tex-math id="M21"〉\begin{document}${{\rm{N}}_{{2}}}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M21.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M21.png"/〉〈/alternatives〉〈/inline-formula〉 appears before the fluorescence of 〈inline-formula〉〈tex-math id="M22"〉\begin{document}${\rm{N}}_2^ + $\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M22.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M22.png"/〉〈/alternatives〉〈/inline-formula〉 and disappears after the fluorescence of 〈inline-formula〉〈tex-math id="M23"〉\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M23.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M23.png"/〉〈/alternatives〉〈/inline-formula〉 has vanished. This is due to the fact that 〈inline-formula〉〈tex-math id="M24"〉\begin{document}${{\rm{N}}_{{2}}}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M24.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M24.png"/〉〈/alternatives〉〈/inline-formula〉 can be ionized into 〈inline-formula〉〈tex-math id="M25"〉\begin{document}${\rm{N}}_{{2}}^{{ + }}{{(}}{{\rm{B}}^{{2}}}\Sigma_{\rm{u}}^{{ + }})$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M25.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M25.png"/〉〈/alternatives〉〈/inline-formula〉 at the position of high enough laser intensity, thus emitting fluorescence of 〈inline-formula〉〈tex-math id="M26"〉\begin{document}${\rm{N}}_2^ + $\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M26.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M26.png"/〉〈/alternatives〉〈/inline-formula〉. However, the laser energy is not enough to ionize nitrogen at the beginning and end of laser transmission, but it can generate 〈inline-formula〉〈tex-math id="M27"〉\begin{document}${\rm{N}}_2^ * $\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M27.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M27.png"/〉〈/alternatives〉〈/inline-formula〉, which emits nitrogen fluorescence through the process of intersystem crossing 〈inline-formula〉〈tex-math id="M28"〉\begin{document}${\rm{N}}_2^*\xrightarrow{{{\rm{ISC}}}}{{\rm{N}}_2}({{\rm{C}}^3}\Pi _{\rm{u}}^ + )$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M28.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M28.png"/〉〈/alternatives〉〈/inline-formula〉. The spatial distribution of nitrogen fluorescence emission during femtosecond laser filament formation shows that in the case of short focal length, the intersystem crossing scheme can explain the formation of 〈inline-formula〉〈tex-math id="M29"〉\begin{document}${{\rm{N}}_{{2}}}{{(}}{{\rm{C}}^{{3}}}\Pi _{\rm{u}}^{{ + }})$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M29.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M29.png"/〉〈/alternatives〉〈/inline-formula〉. This research is helpful in understanding the mechanism of nitrogen fluorescence emission.

Abstract: This paper presents the molecular dynamics simulations of atomic structures of nanocrystals (1—3nm).The X-ray diffraction patterns and the radial distribution functions corresponding to the above nanocrystalline structures were also computed.The results show that the interfacial component exhibits short-range order,and the distortion in crystalline component increases with the decrease of grain size.

Abstract: A series of single phase YBa2Cu3Oy samples with various oxygen contents and Tcmid's〉 90K were prepared, and their structures, superconductivities, flux pinning behaviors have been determined and investigated. The experimental results show that the oxygen deficiencies result in enhancements of critical current density Jc and flux pinning force density Fp, moreover, there exists an optimal concentration of okygen deficiencies, corresponding to the maximal enhancemenes of Jc and Fp. Different from the cases of y= 6. 96,6. 83,Jc of y= 6.94,6.86 samples vary unmonotonicly with magnetic field H, correpondingly, the magnetization curves exhibit an abnormal peak known as "fishtail" effect. Fitted with the scaling law, it is found that when 6.83≤y≤6.94, the peak in fp(h) curves appears at the same reduced magnetic field h(≈0. 6). It indicates that the existence of oxygen deficiencies introduces new flux pinning centres in YBa2Cu3Oy.

Abstract: The giant magnetoriesistance (GMR) effects in sandwiched Co/Cu/Co and Co/CuMn/Co structures have been investigated. The GMR oscillates with the spacer thickness for both cases, but nearly antiphased. With diluted Mn atoms in the Cu spacer, the GMR curve as a function of the magnetic field changes a lot, and the saturation/switching field for GMR can be reduced greatly compared with that in Co/Cu/Co systems. This may suggest one way to obtain a highly sensitive GMR.

Abstract: The InyGa1-y As/GaAs superlattice with an InxGa1-x As (xyGA1-yAs interface was narrower than that at the InyGa1-y As/GaAs interface; in InyGa1-yAs alloy layer, the composition near the GaAs/InyGa1-y As interface was larger than that near the other interface. For the first time, we have explained the composition profile in these kinds of superlattices based on the indium segregation theory. In addition, a new strain relaxation model was presented to explain the differences in the smoothness between the two interfaces.