Near and far field

About: Near and far field is a research topic. Over the lifetime, 15922 publications have been published within this topic receiving 220571 citations.

Experimental demonstration of linear and spinning Janus dipoles for polarisation- and wavelength-selective near-field coupling.

Abstract: The electromagnetic field scattered by nano-objects contains a broad range of wavevectors and can be efficiently coupled to waveguided modes. The dominant contribution to scattering from subwavelength dielectric and plasmonic nanoparticles is determined by electric and magnetic dipolar responses. Here, we experimentally demonstrate spectral and phase selective excitation of Janus dipoles, sources with electric and magnetic dipoles oscillating out of phase, in order to control near-field interference and directional coupling to waveguides. We show that by controlling the polarisation state of the dipolar excitations and the excitation wavelength to adjust their relative contributions, directionality and coupling strength can be fully tuned. Furthermore, we introduce a novel spinning Janus dipole featuring cylindrical symmetry in the near and far field, which results in either omnidirectional coupling or noncoupling. Controlling the propagation of guided light waves via fast and robust near-field interference between polarisation components of a source is required in many applications in nanophotonics and quantum optics.

Plasmonic enhanced infrared detector element

Abstract: Electromagnetic radiation detector elements and methods for detecting electromagnetic radiation, in particular, infrared radiation, are provided The electromagnetic radiation detector element can include an electromagnetic radiation detector and a plasmonic antenna disposed over the electromagnetic radiation detector The plasmonic antenna can include a metal film, a sub-wavelength aperture in the metal film, and a plurality of circular corrugations centered around the sub-wavelength aperture

Annular (HSURIA) resonators: some experimental studies including polarization effects

Abstract: A repetitively pulsed CO2 laser facility was developed for testing annular resonators. The large-aperture device exhibits generally uniform gain over an annular region of 18-cm o.d. and 10-cm i.d. The half-symmetric unstable resonator with internal axicon (HSURIA) was tested at equivalent Fresnel numbers up to 4.5. This resonator design incorporates a W-axicon mirror beam compactor that transforms a cylindrical-mode region into an annular-mode region. Two HSURIA configurations were evaluated: (a) with a conical end mirror and (b) with a flat end mirror in the annular leg. With the conical end mirror, the aligned resonator produced a predominantly higher-order azimuthal mode with an on-axis null in the far field. The output was strongly linearly polarized with the electric-field vector tangential to the optic axis in both the near and far fields. The higher-order tangentially polarized mode appears to be the result of a geometric polarization scrambling effect caused by the conical end mirror. The boundary conditions for the conical or W-axicon mirrors imply that the radial electric field has a 180° phase shift on reflection, whereas the tangential component is unchanged. Thus, a tangentially polarized mode is self-reproducing, but a linearly polarized mode is not. To eliminate the polarization scrambling effect in the HSURIA, the conical end mirror was replaced with a flat end mirror. The HSURIA with a flat end mirror produced a central spot in the far field that indicated an l = 0 mode with no spatial variations in polarization. Beam quality was measured in terms of the ratio n2 of the theoretical (geometric-mode) power transmitted through an aperture of the central lobe diameter to the observed power; n2 values as low as 1.2 were obtained. The variation of beam quality with tilt of the flat end mirror indicated a factor of 2 degradation in n2 for a 20-μrad tilt, which is in good agreement with theory.

Two-Dimensional Electromagnetic Scattering of Non-Plane Incident Waves by Periodic Structures

Abstract: —This paper proposes the pseudo-periodic Fourier transform to analyze the electromagnetic scattering from periodic structures with non-plane wave incidence The pseudo-periodic Fourier transform converts arbitrary field components into pseudo-periodic functions and the conventional grating theories based on the Floquet theorem become applicable The inverse transform is given by integrating with respect to the transform parameter over a finite interval and the near field analysis requires numerical integration Some application examples are numerically examined and the results show good convergence

Scattering of Electromagnetic Waves by a Cylinder Moving Along its Axis

Abstract: The scattering of a time-harmonic, linearly polarized plane electromagnetic wave by a cylinder uniformly moving along its axis is discussed. The formalism is relativistically exact, and explicit forms are provided for first-order velocity effects. Consideration is given to both a cylinder moving in free space, using the procedure suggested by Einstein, and two refractive media; it is veritied that the first case is a special case of the second one. Thin scatterers are considered and it is shown that no first-order velocity effects are present. For a moving medium, having in its rest frame the same constitutive parameters as the surrounding medium, it is shown that the velocity-independent part vanishes, but scattered fields of the first order in the velocity are still present. Moreover, these waves appear with the opposite polarization (compared to the incident wave).