The nature of light as an electromagnetic wave with transverse components has been confirmed using optical polarizers, which are sensitive to the orientation of the electric field. Recent advances in nanoscale optical technologies demand their magnetic counterpart, which can sense the orientation of the optical magnetic field. Here we report that subwavelength metallic apertures on infinite plane predominantly sense the magnetic field of light, establishing the orientation of the magnetic component of light as a separate entity from its electric counterpart. A subwavelength aperture combined with a tapered optical fibre probe can also serve as a nanoscale polarization analyser for the optical magnetic field, analogous to a nanoparticle sensing the local electric polarization. As proof of its functionality, we demonstrate the measurement of a magnetic field orientation that is parallel to the electric field, as well as a circularly polarized magnetic field in the presence of a linearly polarized electric field.

Nature of light as an electromagnetic wave with transverse components has been confirmed using optical polarizers, which are sensitive to the electric field orientation only. Recent advances in optical technologies in nanometer scale demand their magnetic counterpart: optical magnetic polarizers. Here we experimentally establish the optical magnetic field polarization as a separate entity from the electric field polarization by showing that subwavelength circular metallic apertures predominantly sense the magnetic field component of light.

We have measured local electric field polarization vectors in 3-dimensional space on the nanoscale. A radial polarized light is generated by using a radial polarization converter and focused by an objective lens. Gold nanoparticle functionalized tips are used to scatter the focused field into the far-field region. Two different methods, rotational analyzer ellipsometry and Stokes parameters, are used in determining the polarization state of the scattered light. Two methods give consistent results with each other. Three dimensional local polarization vectors could be reconstructed by applying back transformation of the fully characterized polarizability tensor of the tip.

Using near-field scanning optical microscopy and ultrafast laser spectroscopy, we study the linear optical properties of subwavelength nanoslit and nanohole arrays in metal films, which are prototype structures for novel plasmonic metamaterials. Near-field microscopy provides direct evidence for surface plasmon polariton (SPP) excitation and allows for spatial imaging of the corresponding SPP modes. By employing spectral interferometry with ultrashort 11-fs light pulses, we directly reconstruct the temporal structure of the electric field of these pulses as they are transmitted through the metallic nanostructures. The analysis of these data allows for a quantitative extraction of the plasmonic band structure and the radiative damping of the corresponding SPP modes. Clear evidence for plasmonic band gap formation is given. Our results reveal that the coherent coupling between different SPP modes can result in a pronounced suppression of radiative SPP damping, increasing the SPP lifetime from 30 fs to more than 200 fs. These findings are relevant for optimizing and manipulating the optical properties of novel nano-plasmonic devices.

The behaviour of nanoscale optical devices in a variety of burgeoning research areas, such as photonic crystals1,2,3,4, near-field microscopy5,6,7, surface plasmonics8,9,10,11 and negative index of refraction materials12,13,14,15,16, is governed by strongly localized electromagnetic waves. Although such light waves are analogous to the localized electronic wavefunctions that determine the properties of solid-state quantum devices, unlike matter waves, these optical fields are vectorial in nature, and their orientation and magnitude vary on a subwavelength scale. In order to obtain a complete description of light in nanoscale devices, it is therefore crucial to be able to map the field vectors with subwavelength resolution. Thus far, local field vectors have mostly been studied by theoretical means. Here, we describe and demonstrate the first experimental mapping of vector fields of light on the nanoscale. By directly accessing the local field in its entirety, new capabilities and applications in nanophotonics may emerge.

We report the first measurement of blue shifted plasmonic bandgap structures. Issues concerning the Rayleigh wavelength, Wood's anomaly, surface plasmonic and Fabry-Perot resonances are clarified.