RESUMEN
Improving the image quality of small particles is a classic problem and especially challenging when the distance between particles are below the optical diffraction limit. We propose a imaging system illuminated with radially polarized light combined with a suitable substrate that contains a thin dielectric layer to demonstrate that the imaging quality can be enhanced. The coupling between the evanescent wave produced in a designed thin dielectric layer, the small particles and the propagating wave forms a mechanism to transfer sub-wavelength information about the particles to the far field. The smallest distinguished distance reaches to 0.634λ, when the imaging system is composed of a high numerical aperture (NA=0.9) lens and the illumination wavelength λ = 632nm, beyond the diffraction limit 0.678λ. The lateral resolution can be further improved by combining the proposed structure with superresolution microscopy techniques.
RESUMEN
Optical angular momenta (AM) have attracted tremendous research interest in recent years. In this paper we theoretically investigate the electromagnetic field and angular momentum properties of tightly focused arbitrary cylindrical vortex vector (CVV) input beams. An absorptive particle is placed in focused CVV fields to analyze the optical torques. The spin-orbit motions of the particle can be predicted and controlled when the influences of different parameters, such as the topological charge, the polarization and the initial phases, are taken into account. These findings will be helpful in optical beam shaping, optical spin-orbit interaction and practical optical manipulation.
RESUMEN
Rigorous vectorial focusing theory is used to study the imaging of small adjacent particles with a confocal laser scanning system. We consider radially polarized illumination with an optimized amplitude distribution and an annular lens to obtain a narrower distribution of the longitudinal component of the field in focus. A polarization convertor at the detector side is added to transform radial polarization to linear polarization in order to make the signal detectable with a single mode fiber.
RESUMEN
Light scattering by a grating of the metal (Ag)-coated nanocylinders supported on the dielectric substrate is investigated using an accurate and rigorous formulation based on the recursive algorithm combined with the lattice sums technique. The proposed approach could be applied easily to the various configurations of the grating composed of the metal or metal-coated nanocylinders with different types and locations of the excitation sources. Special attention is paid to the three types of resonances: (a) surface plasmon resonances associated with the metal nanocylinders, (b) Rayleigh anomalies related with the periodic nature of the grating, and (c) resonances due to the coupling between the grating and the dielectric substrate. Near-field distribution of the magnetic field, which is parallel to the axis of the nanocylinders, is investigated numerically. Physical insight is given to the localization of the field along the interfaces of the metal nanocylinders, formation of the strong reflected field by the grating, and the field enhancement at the surface of the dielectric substrate. The accuracy of the numerical analyses has been tested based on the principle of the energy conservation. All these features are technologically important and have wide practical application from the viewpoint of the flexible design and fabrication of the plasmonic optical devices.
