Near field and far field scattering of surface plasmon polaritons by one-dimensional surface defects

A rigorous formulation for the scattering of surface plasmon polaritons (SPP) from a one-dimensional surface defect of any shape that yields the electromagnetic field in the vacuum half-space above the vacuum-metal interface is developed by the use of an impedance boundary condition. The electric and magnetic near fields, the angular distribution of the far-field radiation into vacuum due to SPP-photon coupling, and the SPP reflection and transmission coefficients are calculated by numerically solving the k-space integral equation upon which the formulation is based. In particular, we consider Gaussian-shaped defects and study the dependence of the above mentioned physical quantities on their 1/e half-width a and height h. SPP reflection is significant for narrow defects; maximum reflection (plasmon mirrors) is achieved for a~lambda/10. For increasing defect widths, protuberances and indentations behave differently. The former give rise to a monotonic increase of radiation at the expense of SPP transmission for increasing defect half-width. Indentations exhibit a significant increase of radiation (decrease of SPP transmission) for half-widths of the order of or smaller than the wavelength, but tend to total SPP transmission in an oscillatory manner upon further increasing the half-width. Light-emitters might thus be associated with either wide indentations, or protuberances with widths that are of the order of or smaller than the wavelength.Comment: REVTeX 3.1, 10 pages with 9 EPS figures (epsf macro

Quantifying Non-circular Streaming Motions in Disc Galaxies

High-quality velocity maps of galaxies frequently exhibit signatures of non-circular streaming motions. We here apply the software tool, "velfit" recently proposed by Spekkens & Sellwood, to five representative galaxies from the THINGS sample. We describe the strengths and weaknesses of the tool, and show that it is both more powerful and yields results that are more easily interpreted than the commonly used procedure. We demonstrate that it can estimate the magnitudes of forced non-circular motions over a broad range of bar strengths from a strongly barred galaxy, through cases of mild bar-like distortions to placing bounds on the shapes of halos in galaxies having extended rotation curves. We identify mild oval distortions in the inner parts of two dwarf galaxies, NGC 2976 and NGC 7793, and show that the true strength of the non-axisymmetric gas flow in the strongly barred galaxy NGC 2903 is revealed more clearly in our fit to an optical Halpha map than to the neutral hydrogen data. The method can also yield a direct estimate of the ellipticity of a slowly-rotating potential distortion in the flat part of a rotation curve, and we use our results to place tight bounds on the possible ellipticity of the outer halos of NGC 3198 and NGC 2403.Comment: 12 pages, 8 color figures, to appear in MNRAS. Version 2 of the software can be downloaded from http://www.physics.rutgers.edu/~spekkens/velfit

Hypernuclear Physics at PANDA

Hypernuclear research will be one of the main topics addressed by the PANDA experiment at the planned Facility for Anti-proton and Ion Research FAIR at Darmstadt, Germany. A copious production of Xi-hyperons at a dedicated internal target in the stored anti-proton beam is expected, which will enable the high-precision gamma-spectroscopy of double strange systems for the first time. In addition to the general purpose PANDA setup, the hypernuclear experiments require an active secondary target of silicon layers and absorber material as well as high purity germanium (HPGe) crystals as gamma-detectors. The design of the setup and the development of these detectors is progressing: a first HPGe crystal with a new electromechanical cooling system was prepared and the properties of a silicon strip detector as a prototype to be used in the secondary target were studied. Simultaneously to the hardware projects, detailed Monte Carlo simulations were performed to predict the yield of particle stable hypernuclei. With the help of the Monte Carlo a procedure for Lambda-Lambda-hypernuclei identification by the detection and correlation of the weak decay pions was developed.Comment: prepared for the International Conference on Exotic Atoms and Related Topics (EXA2011), Vienna, Sept. 5-9, 201