Abstract
A confined, evanescent nano-source based on the excitation of Surface Plasmon Polaritons (SPP) on structured thin metal films is proposed. With the help of a suitable cavity, we numerically demonstrate that it is possible to trap SPP over a spatial region smaller than the diffraction limit. In particular, the enhanced plasmonic field associated with the zero-order cavity mode can be used as a virtual probe in scanning near-field microscopy systems. The proposed device shows both the advantages of a localized, non-radiating source and the high sensitivity of SPP-based sensors. The lateral resolution is limited by the lateral extension of the virtual probe. Results from simulated scans of small objects reveal that details with feature sizes down to 50 nm can be detected.
Highlights
One of the basic requirements of many super-resolving imaging systems is to illuminate the sample with a highly confined optical field
Well-established Scanning Near-field Optical Microscopy (SNOM) techniques can accomplish this in different ways
We propose a flat surface surrounded by a pair of sinusoidal gratings acting as Distributed Bragg Reflectors (DBR) for surface waves
Summary
One of the basic requirements of many super-resolving imaging systems is to illuminate the sample with a highly confined optical field. It is possible to obtain a localized field by tightly focusing higher-order Hermite-Gaussian beams on metal tips, which can be employed as nano-sources [1]. The main drawback in the exploitation of such a field is the necessity of the probe itself, which is, in general, fragile and difficult to reproduce on a large scale One solution to this problem was suggested by Grosjean et al [8, 9], who proposed the use of virtual (or immaterial) tips, in near-field microscopy. Experimental setup allowed the generation of an evanescent, non-diffracting and longitudinally polarized field confined over a circular region of diameter ∼ λ /5, to be used for sample illumination Another realization of a non-radiating source is presented in Ref. This method is suited for studying this kind of problem since it allows smooth grating profiles to be considered without performing any multi-layer structure discretization [12, 26, 27, 28]
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