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 (SP P's) from a one-dimensional surface defect of any shape that yields the ele ctromagnetic field in the vacuum half-space above the vacuum-metal interfac e is developed by the use of an impedance boundary condition. The electric and magnetic near fields, the angular distribution of the far-field radiati on into vacuum due to SPP-photon coupling, and the SPP reflection and trans mission coefficients are calculated by numerically solving the k-space inte gral equation upon which the formulation is based. In particular, we consid er Gaussian-shaped defects (either protuberances or indentations) and study the dependence of the above-mentioned physical quantities on their lie hal f-width a and height h. SPP reflection is significant for narrow defects (a less than or equal to lambda/5, for either protuberances or indentations, where lambda is the wavelength of the SPP); maximum reflection (plasmon mir rors) is achieved-for a approximate to lambda/10. For increasing defect wid ths, protuberances and indentations behave differently. The former give ris e to a monotonic increase of radiation at the expense of SPP transmission f or increasing defect half-width. However, indentations exhibit a significan t increase of radiation (decrease of SPP transmission) for half-widths of t he order of or smaller than the wavelength, but tend to total SPP transmiss ion in an oscillatory manner upon further increasing the half-width. Both t he position of the maximum radiation and the oscillation period depend on t he defect height, which in all other cases only affects the process quantit atively. Light emitters might thus be associated with either wide indentati ons or protuberances with widths that are of the order of or smaller than t he wavelength. [S0163-1829(99)01735-X].