Plasmonic near-field probe using the combination of concentric rings and conical tip under radial polarization illumination

We numerically study a plasmonic near-field probe design that integrates a sharp metallic conical tip at the center of a multiple concentric ring plasmonic lens under radially polarized illumination. Due to the symmetry match between the plasmonic structure and the illumination polarization, surface plasmon waves can be efficiently excited and focused by the annular ring structure towards the conical tip at the center. The metallic tip further localizes and enhances the plasmonic field at the tip apex. With a 5 mu m tip height and 5 nm tip radius, spatial resolution with the full width at half-maximum of 5.97 nm and electric energy enhancement of 7.29 x 10(4) can be achieved with 632.8 nm optical excitation. The enhancement factor of this probe design does not strongly depend on the tip cone angle and the excitation wavelength. The strong local field enhancement at the end of the tip and its less stringent fabrication requirements make this probe design very attractive for a broad range of applications in near-field optical imaging.