Observation of localized optical near‐field generated by submicron two‐hole structure for novel SNOM probe

Abstract

AbstractA novel concept for the fabrication of a submicrometer‐structured probe tip for application in scanning near‐field optical microscopy (SNOM) based on a metalized optical fiber and a focused ion beam (FIB) milling is presented and investigated experimentally. This concept has the potential to enable a novel SNOM probe having a reproducible characteristic in the generation of intense and highly localized optical near‐field at the probe tip. As the simplest case designed by the boundary element method (BEM), a fine structure, which sandwiches a small projecting portion between a pair of 100‐nm2 holes, was fabricated by FIB in a 200‐nm silver thin film on a flattened end face of the single‐mode optical fiber. This unique structure was backlit by light from an Ar+ ion laser with a wavelength of 514.5 nm, which passes along the fiber core, and combined optical and topographical measurements for detecting the localized optical near‐field around the holes. A sample scan was performed using a modified SNOM system employing a dielectric spherical probe of 500 nm in diameter, which was illuminated by the evanescent field arising from the total internal reflection of He‐Ne laser light with a wavelength of 632.8 nm. As a result, a small dimple corresponding to the two‐hole structure was observed in the topographic image and a bright spot having high locational correlation with the dimple was simultaneously recorded in the optical image. Further study is required to determine the dependence of the optical near‐field intensity and its localization on the submicrometer two‐hole structure. Copyright © 2008 John Wiley & Sons, Ltd.