2019

Resonant Coupling and Gain Singularities in Metal/Dielectric Multishells: Quasi-Static Versus T‑Matrix Calculations

We investigate the resonant gain response in doped multishell hybrid nanoparticles made of concentric and alternated doped dielectric and metal shells. In particular, we compare the enhanced extinction properties calculated in a quasi-static approximation with accurate light scattering calculations in the T-matrix formalism.

We show that, even for small hybrid particles, a difference in the calculated optoplasmonic mode yields a dramatic change in the resonant coupling with the doped molecular system. Thus, although a simple dipole approach gives a fast qualitative view of the multishell gain-assisted response, a complete light scattering framework is crucial for a quantitative investigation of these hybrid nanosystems.

J. Phys. Chem. C 2019, 123, 48, 29291-29297

Near-field imaging of surface-plasmon vortex-modes around a single elliptical nanohole in a gold film

We present scanning near-field images of surface plasmon modes around a single elliptical nanohole in 88 nm thick Au film. We find that rotating surface plasmon vortex modes carrying extrinsic orbital angular momentum can be induced under linearly polarized illumination. The vortex modes are obtained only when the incident polarization direction differs from one of the ellipse axes.

The presence of the vortex mode is determined by the rotational symmetry breaking of the system. The configuration producing vortex modes corresponds to a nonzero total topological charge (+1).

Scientific Reports, volume 9, Article number: 5320 (2019)

Chiral optical tweezers for optically active particles in the T-matrix formalism

Here we extend T-matrix formalism to the modeling of chiral optomechanics and optical tweezers where chiral light is used for optical manipulation and trapping of optically active particles. We first use the Bohren decomposition to deal with the light scattering of chiral light on optically active particles.

Thus, we show analytically that all the observables (cross sections, asymmetry parameters) are split into a helicity dependent and independent part. We also apply this chiral T-matrix framework to optical tweezers where a tightly focused chiral field is used to trap an optically active spherical particle, calculate the chiral behaviour of optical trapping stiffnesses and their size scaling, and extend calculations to chiral nanowires and clusters of astrophysical interest. Such general light scattering framework opens perspectives for modeling optical forces on biological materials where optically active amino acids and carbohydrates are present.

Scientific Reports, volume 9, Article number: 29 (2019)

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