Plasmonic scattering from single subwavelength holes: Separating the electric and magnetic contributions

Cutting-edge nanophotonic systems are increasingly displaying a magnetic, as well as an electric optical response that, for example, is integral to phenomena such as negative-index of refraction [1]. For these applications, and for many others such as those based on extraordinary optical transmission [2], the details of the response are important. For example, for negative index metamaterials the spectral location of the magnetic and electric resonances determines the window in which the material has n <; 0. It is therefore surprising that for holes, which are the basic elements of many nanophotonic systems, there has been no systematic study that separates and explains both their electric and magnetic responses. In fact, it was only last year that the electric contribution to the scattered field that results from a surface wave - subwavelength hole interaction was quantified [3]. Here we report on the explicit separation of the electric and magnetic contributions to plasmonic scattering from a series of subwavelength holes in optically thick gold films. We use a combination of rigorous electromagnetic theory and high resolution phase-sensitive near-field microscopy to determine the electric and magnetic polarizabilities of holes with diameters <; 1 μm, for a vacuum wavelength of 1550 nm.