Decoupling absorption and emission processes in super-resolution localization of emitters in a plasmonic hotspot

TL;DR

This paper introduces a method to accurately locate emitters near plasmonic antennas by spectrally decoupling absorption and emission processes, enabling detailed mapping of electromagnetic fields and local density of states at nanometer resolution.

Contribution

The study proposes using a large Stokes shift dye to separate absorption from emission, allowing precise localization of emitters and mapping of electromagnetic properties near plasmonic structures.

Findings

Spectral decoupling enables accurate emitter localization.

Method allows mapping of EM field and LDOS at nanometer scale.

Technique improves understanding of emitter-antenna interactions.

Abstract

The absorption process of an emitter close to a plasmonic antenna is enhanced due to strong local electromagnetic (EM) fields. The emission process, if resonant with the plasmonic system, re-radiates to the far-field by coupling with the antenna due to the availability of plasmonic states. This increases the local density of states (LDOS), effectively providing more, or alternate, pathways for emission. Through the mapping of localized emission events from single molecules close to plasmonic antennas, performed using far-field data, one gains combined information on both the local EM field strength and the LDOS available. The localization from these emission-coupled events generally do not, therefore, report the real position of the molecules, nor the EM enhancement distribution at the illuminating wavelength. Here we propose the use of a large Stokes shift fluorescent molecule in order to spectrally decouple the emission process of the dye from the plasmonic system, leaving only the absorption strongly in resonance with the enhanced EM field in the antennas vicinity. We show that the real position of the emitters in this complex, but interesting, scenario can be found directly. Moreover, we demonstrate that this technique provides an effective way of exploring either the EM field or the LDOS with nanometre spatial resolution.