Open AccessSimulation of a metallic SNOM tip illuminated by a parabolic mirror
Author(s) -
Josip Mihaljević,
Christian Hafner,
Alfred J. Meixner
Publication year - 2013
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.21.025926
Subject(s) - optics , bessel beam , near field scanning optical microscope , surface plasmon , bessel function , physics , microscope , field (mathematics) , axicon , near and far field , near field optics , ray tracing (physics) , optical microscope , plasmon , laser beams , laser , scanning electron microscope , mathematics , pure mathematics
We investigate numerically a Scanning Near field Optical Microscope (SNOM) that uses a Parabolic Mirror (PM) to focus a radially polarized beam on a metallic tip. In order to overcome problems--like overestimated near fields or resonances--that arise when only considering finite tips, we have introduced a semi-infinite continuation of the tip, which incorporates the analytic solution of surface waves. For a realistic modeling the right description of the incident field is essential and we have complied with this requirement by a Bessel expansion of the focal fields, which is also applicable to an aplanatic objective. The established numerical model is used for an extensive study of model parameters like tip geometry, illumination directions and tip materials (Ag, Au, Al and Cu). Compared with a simplified inverted microscope configuration, the PM setup shows an increased field enhancement (factor of 2-2.5), which can be ascribed to the efficient coupling of the exciting field to tip surface plasmons.