KEYWORDS: Nanostructures, Plasmonics, Near field scanning optical microscopy, Near field, Metals, Near field optics, Solids, Gold, Finite element methods, Glasses
We develop a method based on the reciprocity and Green function to efficiently obtain the far-field pattern of dipole emitters around plasmonic nanostructures. Applying this method to air hole arrays fabricated on metal films, we reveal their plasmonic characteristics in the near-field scanning optical microscopy. Modeling scanning-probe tips as surface plasmon launchers, we clarify the orientation effect of their equivalent dipoles and also how these effective dipoles contribute to the excitation of different plasmonic modes, resulting in distinguishable characteristics in the far-field imaging. The outcomes of our calculations are validated with the experimental data from a high-resolution raster scanning nano-focusing plasmonic tip. Satisfactory agreements between the model and measurements are demonstrated.
KEYWORDS: Metals, Plasmonics, Near field scanning optical microscopy, Surface plasmons, Spatial resolution, Finite-difference time-domain method, Near field, Near field optics, Silica, Gold
Near-field scanning optical microscopy (NSOM) offers subwavelength optical resolution beyond the diffraction limit, enabling practical applications in optical imaging, sensing and nanolithography. However, due to the sub-100 nm size of apertures, conventional NSOM aperture probes suffer from the constrains of the strong attenuation of the throughput and limited the spatial resolution. To solve the problem, we designed a novel scheme for apertureless plasmonic probes with radial internal illumination. Employing non-periodic multi-rings geometry for plasmonic excitations, surface plasmons adiabatically nanofocuse energy at tip and the full width at half maximum of the optimal design is ∼18 nm. The proposed probe was optimized with 2D finite-difference time-domain (FDTD) analysis and realistic parabolic probe geometries. Comprehensive electromagnetic simulation shows that the optimal probe feature obeys Fabry-Pérot condition on the plasmonic metallic wall, giving rise to substantial field enhancement up to 6 orders of magnitude greater than conventional aperture probes without degrading its spatial resolution. We fabricated the proposed probe which possesses apex angle (∼ 22 degree) and tip radius (∼ 30 nm). Finally, the proposed near field plasmonic probe effectively combining the high resolution of apertureless probes with high throughput can enable the proposed plasmonic NSOM probe as a practical tool for applications in near field optical microscopy.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.