Super-resolution optical microscopic imaging using a structure of surface plasmon resonant cavity

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We report on an observation of a novel super-resolution optical microscopic imaging technique using a surface plasmon resonant cavity (SPRC) in which surface plasmonic waves (SPWs) with a much larger wave vector than that of either the direct illumination light of the same frequency or the SPWs without the SPRC structure are generated to serve as the illumination of the microscopy. Numerical results show that an imaging resolution of 21 nm can be achieved based on the proposed SPRC method under an illumination of 532 nm light, which is 10.4-fold, 4.4-fold or 4.1-fold better than that of conventional high numerical aperture fluorescence microscopy, grating structured illumination microscopy using proximity projection scheme or conventional surface plasmon excitation, respectively. It is also found that the wave vector of the SPRC structure and hence the resolution of the microscopy can be tunable by varying either the cavity height or the thickness of the cavity wall (i.e., silver thin film). The physical origin of the much enhanced resolution and also the tunability of the proposed method are analytically confirmed by the dispersion relation derived from the SPRC system.