Experimental confirmation at visible light wavelengths of the backscattering enhancement phenomenon of the photonic nanojet

Seungmoo Yang,Allen Taflove,Vadim Backman

doi:10.1364/oe.19.007084

Abstract

We report what we believe is the first experimental confirmation at visible light wavelengths of the backscattering enhancement phenomenon of the photonic nanojet. A specially designed sample stage consisting of a multilayered sandwich of glass, solid polydimethylsiloxane (PDMS), and liquid PDMS, permitted the precise positioning of a gold nanoparticle of diameter between 50 and 100 nm within the nanojet emitted by a 4.4 μm diameter BaTiO3 microsphere embedded within the PDMS. We determined that, when the gold nanoparticle is optimally positioned within the nanojet, the backscattering of the microsphere can greatly increase: for example, by 3:1 (200%) for the 50 nm gold nanoparticle. The increased backscattering is strongly dependent upon the illumination wavelength and the numerical aperture of the imaging system, and occurs for nonresonant illuminations of the isolated microsphere. Low objective numerical apertures of approximately 0.075 yield the maximum observed increases in backscattering. The measured data agree well with numerical calculations incorporating Mie-based theory and Fourier optics.

Highlights

The photonic nanojet is a purely linear phenomenon wherein an illuminated dielectric microparticle emits from its shadow-side surface a tightly focused beam which propagates with little divergence for several wavelengths in the external medium [1,2,3]
We report in this paper what we believe is the first experimental confirmation at visible light wavelengths of the backscattering enhancement phenomenon of the photonic nanojet
Using a three-axis hydraulic micromanipulator, the top solid PDMS layer was positioned to move one of the gold nanoparticles bound to its bottom surface toward the center axis of the microsphere located in the solid PDMS layer below

Summary

Introduction

The photonic nanojet is a purely linear phenomenon wherein an illuminated dielectric microparticle emits from its shadow-side surface a tightly focused beam which propagates with little divergence for several wavelengths in the external medium [1,2,3]. To the best of our knowledge, there has not yet been a direct experimental verification and measurement of this phenomenon at any visible light wavelength Such verification and measurement is required to help realize proposed technology applications in nanoparticle detection/sizing and ultrahigh-density optical data storage [12,13]. To this end, we report in this paper what we believe is the first experimental confirmation at visible light wavelengths of the backscattering enhancement phenomenon of the photonic nanojet. The measured data agree well with numerical calculations incorporating Mie-based theory and Fourier optics

Optical imaging experiment sample platform

Theoretical backscattering spectrum—ideal plane-wave illumination

Backscattering enhancement simulation tool

Backscattering enhancement measurements

Findings

Summary and conclusions