Broadband plasmon modulation and high-intensity nanofocusing for high-resolution nanoscale imaging using Fabry-Pérot probes.

Surface plasmon polariton probes have important applications in super-resolution imaging and sensing. However, conventional probes often rely on complex radially polarized light excitation and struggle to achieve high-intensity electric field enhancement localized at the probe tip, which limits their practical performance. This paper proposes a double-slit plasmonic platform-based fiber probe that enables efficient nanofocusing under linearly polarized light by integrating the Fabry-Pérot interference enhancement mechanism of the platform-based structure with the polarization control function of the asymmetric half-ring slit. We introduce an innovative sleeve ring etching technique that increases the probe tip curvature by more than an order of magnitude while also addressing the issue of uncontrollable morphology in conventional probe fabrication. Experimental results demonstrate that the proposed probe exhibits an electric field strength at the probe tip that is six times higher than that of an asymmetric double-slit probe at a wavelength of 633 nm. Furthermore, it maintains stable focusing across a broadband range from 580 nm to 800 nm, with particularly significant enhancement in the short-wavelength region. Additionally, this probe achieves a resolution of 28.6 nm in optical imaging experiments, enabling simultaneous characterization of both morphological and optical properties of deep subwavelength-sized samples under ambient conditions.