Nanoscale optical interferometry with incoherent light.

Dongfang Li,Jing Feng,Domenico Pacifici

doi:10.1038/srep20836

Dongfang Li, Jing Feng + Show 1 more

Open Access

https://doi.org/10.1038/srep20836

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Journal: Scientific Reports	Publication Date: Feb 16, 2016
Citations: 16	License type: CC BY 4.0

Affiliation: Brown University, Providence College

Abstract

Optical interferometry has empowered an impressive variety of biosensing and medical imaging techniques. A widely held assumption is that devices based on optical interferometry require coherent light to generate a precise optical signature in response to an analyte. Here we disprove that assumption. By directly embedding light emitters into subwavelength cavities of plasmonic interferometers, we demonstrate coherent generation of surface plasmons even when light with extremely low degrees of spatial and temporal coherence is employed. This surprising finding enables novel sensor designs with cheaper and smaller light sources, and consequently increases accessibility to a variety of analytes, such as biomarkers in physiological fluids, or even airborne nanoparticles. Furthermore, these nanosensors can now be arranged along open detection surfaces, and in dense arrays, accelerating the rate of parallel target screening used in drug discovery, among other high volume and high sensitivity applications.

Highlights

Optical interferometry has empowered an impressive variety of biosensing and medical imaging techniques
Optical interferometry based on surface plasmon polaritons (SPPs) has enabled a broad range of technical advantages[1,2,3,4,5,6], including enhanced light transmission[7,8], all-optical modulation[9], light beaming[10,11,12,13,14], and medical imaging[15]
Plasmonic interferometers consisting of a central hole flanked by three grooves (H-3G) with subwavelength width were fabricated on a 300 nm-thick silver film by focused ion beam milling and coated with a thin (~40 nm) Cr3+:MgO light emitting layer[20,21]

Summary

Introduction

Optical interferometry has empowered an impressive variety of biosensing and medical imaging techniques. By directly embedding light emitters into subwavelength cavities of plasmonic interferometers, we demonstrate coherent generation of surface plasmons even when light with extremely low degrees of spatial and temporal coherence is employed This surprising finding enables novel sensor designs with cheaper and smaller light sources, and increases accessibility to a variety of analytes, such as biomarkers in physiological fluids, or even airborne nanoparticles. In contrast to other implementations of this structure ( known as bullseye10,12–14), here each excited emitter (i.e. Cr3+ ion in MgO) within the nanohole of each interferometer has a high probability to decay by generating SPP waves (with amplitude ESPP, dashed horizontal lines in Fig. 1a; see Supplementary Fig. S2a)[22,23] These SPPs propagate away from the nanohole and are partially reflected back[24,25] by the subwavelength grooves toward the nanohole, where they interfere with the directly emitted light (with amplitude E0, red solid arrow in Fig. 1a), modifying the fluorescence spectra in the far field. The fluorescence spectra transmitted through the nanohole can be modulated by varying the interferometer arm length RG or the refractive index of the dielectric material on the surface, providing for a novel sensing scheme. (See Supplementary Fig. S2 for more details.)

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