The optical near-field of an aperture tip

Abstract

We use fluorescent nanospheres as scalar detectors for the electric-field intensity in order to probe the near-field of an optical tip used in aperture-type near-field scanning optical microscopy (NSOM). Surprisingly, the recorded fluorescence images show two intensity lobesif the sphere diameter is smaller that the aperture diameter, as expected only in the case of vector detectors like single molecules. We present a simple but realistic, analytical model for the electric field created by light emitted by a NSOM tip which is quantitative agreement with the experimental data.A crucial step towards the development of nanoscale optoelectronic devices from building blocks like single molecules, semiconductor nanocrystals, or quantum dots is the study of their behavior under optical stimulation. On these length scales, near-field effects and diffraction phenomena play a major role both for the interaction of such subwavelength structures with incident light as well as for the communication pathways

Near-field microscopy with a single-photon point-like emitter: Resolution versus the aperture tip?

“…While the far-field generated by the aperture (i.e., for kR ≫ 1) is still in a good approximation described by a dipolar behavior, as confirmed experimentally [44] and theoretically [45,46], the near-field deviates strongly from this simplified assumption. This has been confirmed in several studies [5,7,[47][48][49][50]). Therefore, another approach must be developed.…”

“…Yet one of the most fundamental issue with NSOM concerns the optical resolution available with a given system. Current systems based on aperture-NSOM [1] with a hole at the apex of a metal-coated conical tip are fundamentally limited by the size of the optical hole [5][6][7]. In order to improve the optical resolution of NSOM and therefore overcome this limitation one could ideally use a point-like emitting source.…”

Review of near-field optics and superlenses for sub-diffraction-limited nano-imaging

“…More rigorous electromagnetic calculations of the field distribution of a subwavelength aperture are given by Bethe 72 and Bouwkamp. 73 Similar calculations for the specific case of a SNOM aperture probe were later carried out by Drezet et al 74,75 However, the brief analysis presented here is sufficient to understand the localization of the near-field radiation relevant to the general aperture SNOM concept.…”

Interaction of an Asymmetric Scanning Near Field Optical Microscopy Probe With Fluorescent Molecules

“…A great effort has been devoted throughout the years to the optimization of the near field probe, which plays a major role in the interaction with the sample and in the ultimate attainable resolution [5,6]. Since the proposal of the pioneering aperture structure, based on a metal coated dielectric with a subwavelength aperture left at the end, different options have been explored in order to overcome some of its fundamental drawbacks, i.e., the poor resolution limited by the size of the aperture, the low throughput and the asymmetric near field distribution at the probe apex resulting from the linearly polarized excitation [7][8][9]. Apertureless probes under far field external illumination have been indicated as a possible alternative [10][11][12][13]: although they allow the achievement of high field enhancement and high resolution, the far field illumination creates a strong background potentially deleterious for measurements on sensitive samples, as is the case for, e.g., fluorescent molecules.…”