Collection of transverse and longitudinal fields by means of apertureless nanoprobes with different metal coating characteristics

Abstract

The coupling and transmission of transverse and longitudinal fields into apertureless microfabricated near-field optical probes is investigated. Two kinds of probes with different metal coating roughness are considered. Transverse and longitudinal field distributions are obtained by focusing azimuthally and radially polarized beams produced by means of a liquid crystal plate. The focal plane is scanned using microfabricated probes in a collection mode configuration. It is found that the roughness of the metal coating plays an important role in the coupling strength of transverse fields into the probes: the relative coupling efficiency for transverse fields diminishes with a rough metal coating, while that of longitudinal fields does not.Near-field scanning systems can map optical fields by locally probing small regions of space with suitable nanoprobes. Two of the most well-established scanning near-field optical microscopy (SNOM) techniques make use of probes consisting of metal-coated tapered fibers (or tapered glass capillaries) used as light collectors 1 or metal (or silicon) tips used as light scatterers.2 In mesoscopic optics, the electromagnetic field must be considered in its full vectorial nature and, in order to experimentally obtain complete information on the field amplitude, all three orthogonal components of the electric field vector must be accessible at each step of the scan. Therefore it is necessary to understand the interaction of the probe with not only the transverse components of the field, but also the component oriented longitudinally with respect to the tip axis.In several experiments it has been found that the probe characteristics in imaging transverse and longitudinal fields differ. For example, in the work of Bouhelier et al., 3 the behavior of metallic and dielectric probes in a scattering experiment is presented. It was found that gold tips are more likely to scatter longitudinally polarized fields, while uncoated glass probes are more sensitive to transversely polarized fields. With the advent of micro-machining technology, it has become possible to develop new batch fabrication processes for cantilever-based apertureless SNOM probes. 4,5

A virtual optical probe based on localized Surface Plasmon Polaritons

“…Some investigations based on numerical calculations (see, for example, Ref. [4]) and experimental measurements [5,6,7] revealed that the strongest localization of the emitted field is connected to the presence of a longitudinally polarized field. Nonetheless, the main drawback in the exploitation of such a field is the necessity of the probe itself, which is, in general, fragile and difficult to reproduce on a large scale.…”

Analysis of mode coupling due to spherical defects in ideal fully metal-coated scanning near-field optical microscopy probes

“…This yields an apex angle of 30°, consistent with experimental studies currently being conducted. 12,13 The metal coating is a uniform 50 nm thick layer of aluminum on both the cylindrical and the tapered sections, terminating in a spherical apex of variable diameter (typically 50 nm). Before the subsequent introduction of defects, the probe exhibits a rotational symmetry around the z axis.…”

“…2 To better understand the operating characteristics of this class of probes, a considerable amount of work has been performed to optimize their fabrication, as well as to experimentally measure their performance characteristics. [3][4][5][6][7][8] In particular, the properties of the metal coating 9,10 and the polarization state of the light transiting the probe [11][12][13] have been found to play an important role in the optical properties and performance capabilities of the probe. However, as fabricating and testing large numbers of probes with varying configurations is presently impractical, rigorous electromagnetic modeling of such probes has proven to be a useful complement to experimental work in gaining insight into the propagation of light inside and near such probes.…”

“…Subsequent experimental studies confirmed these numerical results, finding that injecting the radial/longitudinal polarization mode into a microfabricated probe does in fact produce a more strongly localized emitted optical near field, as compared with injecting a purely transversely polarized mode. 12,13 For high-resolution microscopy applications, this strong localization of the emitted field is clearly desirable. The remaining challenge is to simplify the creation and injection of such a radial/longitudinal polarization mode.…”

Near-field visualization of plasmonic lenses: an overall analysis of characterization errors

“…Many SPP-based superlenses were presented recently [7][8][9] as well as resonance immunosensors [10], nanobiosensors [11] and nanoprobes [12]. One of the superlenses consists of a silver film coating on glass with some corrugations [13].…”