A Closer Look at Photonic Nanojets in Reflection Mode: Control of Standing Wave Modulation

Ksenia A Sergeeva,Igor V Minin,Alexander A Sergeev,Oleg V Minin

doi:10.3390/photonics8020054

Abstract

The photonic nanojet phenomenon is commonly used both to increase the resolution of optical microscopes and to trap nanoparticles. However, such photonic nanojets are not applicable to an entire class of objects. Here we present a new type of photonic nanojet in reflection mode with the possibility to control the modulation of the photonic nanojet by a standing wave. In contrast to the known kinds of reflective photonic nanojets, the reported one occurs when the aluminum oxide hemisphere is located at a certain distance from the substrate. Under illumination, the hemisphere generates a primary photonic nanojet directed to the substrate. After reflection, the primary nanojet acts as an illumination source for the hemisphere, leading to the formation of a new reflective photonic nanojet. We show that the distance between the hemisphere and substrate affects the phase of both incident and reflected radiation, and due to constructive interference, the modulation of the reflective photonic nanojet by a standing wave can be significantly reduced. The results obtained contribute to the understanding of the processes of photonic nanojet formation in reflection mode and open new pathways for designing functional optical devices.

Highlights

Along with plasmonics, dielectric photonics [1] is associated with the processes of localization of light and is aimed at increasing the efficiency of the interaction of incident radiation with matter
Calculations were conducted for two positions of a plane wave source with unit intensity: (i) at 3 μm above the hemisphere, which was a compromise between model accuracy and calculation time, and (ii) at 100 nm above the parental microstructure to exclude parasitic interference between the light source and the photonic nanojet (PNJ) generated in reflection mode
It is interesting to note that both types of PNJs have pretty similar properties: (i) the maximum localization intensity is separated from the hemisphere’s surface and located at ≈0.8λ from it; (ii) the PNJ length (Leff), defined as the distance where the maximal PNJ intensity (Imax) decreases by e times, is almost the same and equal to 1.7 μm or ≈3λ

Summary

Introduction

Dielectric photonics [1] is associated with the processes of localization of light and is aimed at increasing the efficiency of the interaction of incident radiation with matter. The progress in this direction contributes to the development of compact optical radiation control devices, opening opportunities for the creation of new sensing structures [2], detection of nano- and microparticles [3,4,5,6], nanoparticle manipulation [7,8], luminescence [9,10] and Raman scattering enhancement [11], and both optical [12,13] and terahertz [14] super-resolution microscopy. These are the typical size and parameters of microlenses [16]

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Results

Conclusion