Active modulation of plasmonic signal with a subwavelength metal/nonlinear dielectric material/metal structure

<正>Light propagation through a metal/nonlinear dielectric material/metal(M-NL-M) structure is numerically studied.The design parameters of the M-NL-M structure are found with the waveguide theory so that the structure only supports the symmetric surface plasmon polaritons(SPP(0)) mode and the antisymmetric surface plasmon polaritons(SPP(1)) mode.The coupling between the two modes within the M-NL-M structure is exploited.Through controlling the propagation constants of the two modes with the intensity-dependent dielectric constant of the nonlinear Kerr material,an effective all-optical control of plasmonic signal modulator can be realized with this M-NL-M structure.     

X射线衍射增强成像中的信息分离和信息处理

人们已经利用X射线的高穿透性,发展了较为成熟的X射线成像理论和技术. X射线成像已经广泛应用于众多领域.传统X射线成像受生物样品中组织间吸收系数差别较小和散射噪声较大两个因素的限制,不易利用这种方法获得生物组织的信息. 衍射增强成像方法不但能将有害的散射噪声滤除,而且能利用样品的折射信息, 是一种具有发展潜力的新成像方法. 本文利用衍射增强成像, 通过在摇摆曲线不同部位成像, 然后对信息处理, 得到了清晰的吸收像、消光(小角散射滤除)像、小角散射(角)宽度像和折射像,最后通过一定的算法将各种成分的像合成, 形成细节部位清晰的合成伪彩色像.     

Local Surface-Plasmons in Nonspherical Metal Nanoparticles

When a small metallic nanoparticle.is irradiated by incident light, the oscillating electric field can cause the conduction electrons to oscillate coherently, which excites the local surface plasmons （LSPs）. As is well known, excited LSPs can gather the energy of incident light to the surface of metallic nanoparticle. Recently, some nonspherical particles, e.g. tetrahedron, are suggested to obtain stronger localized electric field. We employ the discrete dipole approximation method to calculate the optical response of the tetrahedron nanoparticle, including the extinction and distribution of the electric field around the particle. The influences of some parameters, including the nanoparticle size, incident direction and polarization, are investigated to analyse the response modes and to obtain stronger localized electric field.