Broadband and Highly Directional Visible Light Scattering by Laser-Splashed Lossless TiO2 Nanoparticles.

Yinan Zhang,Shiren Chen,Jing Han

doi:10.3390/molecules26206106

Abstract

All-dielectric nanoparticles, as the counterpart of metallic nanostructures have recently attracted significant interest in manipulating light-matter interaction at a nanoscale. Directional scattering, as an important property of nanoparticles, has been investigated in traditional high refractive index materials, such as silicon, germanium and gallium arsenide in a narrow band range. Here in this paper, we demonstrate that a broadband forward scattering across the entire visible range can be achieved by the low loss TiO2 nanoparticles with moderate refractive index. This mainly stems from the optical interferences between the broadband electric dipole and the magnetic dipole modes. The forward/backward scattering ratio reaches maximum value at the wavelengths satisfying the first Kerker’s condition. Experimentally, the femtosecond pulsed laser was employed to splash different-sized nanoparticles from a thin TiO2 film deposited on the glass substrate. Single particle scattering measurement in both the forward and backward direction was performed by a homemade confocal microscopic system, demonstrating the broadband forward scattering feature. Our research holds great promise for many applications such as light harvesting, photodetection and on-chip photonic devices and so on.

Highlights

As the building block of metamaterials and metasurfaces, nanoparticles play a crucial role in controlling light propagation and regulating the light field distribution [1,2]. metal nanoparticles supporting localized surface plasmons have been widely investigated and are found in many applications such as Raman scattering enhancement [3], biosensing [4], metasurfaces [5], nonlinear plasmonics [6,7] and photovoltaics [8,9,10], their large optical losses and lack of magnetic resonances have hindered their further development
All-dielectric nanomaterials have recently emerged as a promising alternative to plasmonic nanoparticles in constituting high-efficiency photonic devices due to the coexistence of electric and magnetic resonances and lower optical losses as well
Directional scattering is an important property in nanoparticles that can be used to make Huygens directional sources [11] and enhance solar energy harvesting [12,13] and photodetector responses

Summary

Introduction

As the building block of metamaterials and metasurfaces, nanoparticles play a crucial role in controlling light propagation and regulating the light field distribution [1,2]. Andrey et al reported the spattering of silicon particles by femtosecond laser ablation and observed the strong magnetic response and high-order dipole resonance [15]. The high refractive index nanoparticles such as Si always have their electric dipole and magnetic dipole resonances separated from each other in the broad spectrum, and this leads to rather narrow band directional scattering. The non-negligible imaginary part of the high refractive index nanoparticles, such as Ge, can red- and blue-shift the electric and magnetic dipole resonances and make them closer, the large optical loss inevitably limits the directivity efficiency. The relatively large optical loss derived from the non-negligible imaginary part of the refractive index of copper oxide and the large scattering strength difference between electric and magnetic dipole resonance empower their forward/backward scattering ratio at a low level. The experimental results are in good agreement with the simulations, with the forward scattering dominating across the entire visible band

Results and Discussions

Effect

Shape of TiO

Conclusions