Directional Optical Sorting of Silicon Nanoparticles

© 2017 American Chemical Society. Optical manipulation of nanoparticles is a topic of great practical importance, with applications in surface science, colloidal chemistry, microfluidics, biochemistry, and medicine. One of the major highlights of this topic is particle sorting, which serves to create monodisperse systems remotely and to separate particles of different composition and size. Here, we analyze optical forces acting on spherical silicon nanoparticles that exhibit high-quality Mie resonances and demonstrate the potential of optical sorting methods for these systems. In particular, we propose multidirectional static sorting of nanoparticles using noncollinear beams with different wavelengths, which results in all-optical separation into an angular spectrum of sizes. We also validate the proposed methods by considering the operation in the presence of Brownian motion and in the evanescent wave configuration

Optical Third-Harmonic Generation in Hexagonal Boron Nitride Thin Films

Hexagonal boron nitride (hBN) is a layered material that exhibits remarkable optical features in the UV, visible, and IR ranges, attractive for applications in modern photonics. Being transparent in a wide spectral range, hBN is now considered an important building block for novel integrated photonic platforms, thus requiring the study of its optical properties. In this work, we report on the measurements of hBN optical cubic nonlinearity χ(3) equal to 8.4 × 10-21 m2/V2 by observing the third-harmonic generation for 1080 nm pump wavelength from mechanically exfoliated hBN flakes with thicknesses varying from 5 to 170 nm. The third-order susceptibility of hBN is close to that of Si3N4 highlighting the potential of hBN for nonlinear applications

Nonlinear symmetry breaking in symmetric oligomers

A novel type of nonlinear symmetry breaking in symmetric plasmonic oligomers is reported. By monitoring the strength of the second-harmonic signal while changing the polarization angle of the pump, we observe nonlinear symmetry breaking as a large variation in the generated nonlinear signal. Importantly, the strongly anisotropic nonlinear response is produced by a symmetric structure with isotropic linear response when rotating polarization. We provide theoretical analysis to describe and characterize this effect. Our finding opens new avenues to reveal and characterize the symmetry of nanoscale structures and molecules and also to remotely monitor variations of near-field patterns produced by symmetric nanostructure

Composite SERS-based satellites navigated by optical tweezers for single cell analysis

Herein, we have designed composite SERS-active micro-satellites, which exhibit a dual role: (i) effective probes for determining cellular composition and (ii) optically movable and easily detectable markers. The satellites were synthesized by the layer-by-layer assisted decoration of silica microparticles with metal (gold or silver) nanoparticles and astralen in order to ensure satellite SERS-based microenvironment probing and satellite recognition, respectively. A combination of optical tweezers and Raman spectroscopy can be used to navigate the satellites to a certain cellular compartment and probe the intracellular composition following cellular uptake. In the future, this developed approach may serve as a tool for single cell analysis with nanometer precision due to the multilayer surface design, focusing on both extracellular and intracellular studies

Selective Third-Harmonic Generation by Structured Light in Mie-Resonant Nanoparticles

We study the third-harmonic generation by structured light in subwavelength silicon nanoparticles which support both electric and magnetic multipolar Mie resonances. By tailoring the vectorial structure of the pumping light, we may control both strength and polarization composition of the excited harmonic fields. In this way, we generate nonlinear fields with radial or azimuthal polarizations by addressing selectively a different type of multipolar Mie resonances, also enhancing or suppressing the optically induced nonlinear magnetic response