Nanofocusing of surface plasmon polariton by a conical metal-coated dielectric probe was investigated numerically using the three dimensional volume integral equation. The basic characteristics of the nanofocused optical fields generated by this probe were investigated in detail. The intensity distribution near the probe tip was found to be very sensitive to the shape of the probe tip. Enhanced local fields interfere near the tip for certain probe tip shapes.
A numerical study of the nanofocusing of surface plasmon polaritons (SPPs) by a pyramidal structure on a rectangular aperture is performed by the volume integral equation method. It is possible to perform nanofocusing using this structure by using a linearly polarized wave as the incident wave. The focusing process of SPPs by the tip of the pyramidal structure has been demonstrated numerically. The characteristics of the focused optical field near the tip have been investigated in detail. It was found to be similar to that of monopole rather than that of a tiny dipole. The optical field at the tip is sensitive to the local shape of the tip. The enhanced intensity on the tip increases with an increase in the aperture width.
Imaging by near-field scanning optical microscopy (NSOM) with a plasmonic gap probe (PGP) is simulated to confirm the operation of the recently proposed PGP. The simulations demonstrate that the probe works in illumination, collection-reflection and collection mode, and that is it not necessary to vibrate the probe tip in order to remove background noise. The resolution of the scanned image is also shown to be approximately equal to the diameter of the probe tip. Furthermore, the throughput of the probe is much higher than conventional aperture probes providing similar resolution. The proposed probe thus has the advantages of both aperture probes and scattering probes, and is expected to have excellent characteristics for use as a scanning probe for NSOM.
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