Orientation averaging of optical chirality near nanoparticles and aggregates

Orientation-averaged light scattering by nanoparticle clusters: far-field and near-field benchmarks of numerical cubature methods

“…These larger clusters typically require higher multipolar orders to describe the overall response of the cluster to inci-dent light about a single origin, resulting in a more intricate angular pattern and a more challenging orientation averaging via numerical cubature. We illustrate such a situation by considering a helical strand of gold nanorods previously studied 24 , similar in size to some recently-proposed self-assembled structures 56 . The structure consists of 5 gold spheroids immersed in water (Fig.…”

“…incident and scattered fields yield analytical formulas for orientation-averaged optical properties. This powerful formalism enables benchmark calculations for various quantities of interest, which include orientation-averaged extinction, scattering and absorption 19,20 , circular dichroism 21 , but also near-field intensity 22 and local degree of optical chirality 23,24 . Although analytical, these orientationaveraged expressions can become quite involved in the case of near-field quantities, requiring the costly evaluation of translation matrices for each evaluation point.…”

Orientation dependence of optical activity in light scattering by nanoparticle clusters

“…denotes the orientation-average of C with respect to the direction of incident light. 46 We assess the angular dependence of the local degree of optical chirality at small distances from a dimer of Si nanospheres (radius r = 150 nm and gap = 10 nm), where multipolar modes can play an important role in the optical spectrum. Fig.…”

“…In contrast, a similar dimer with plasmonic particles would typically show a spatial distribution of peaks of positive and negative signs, weakening the spatial average for analytes uniformly adsorbed on the particle surfaces. 46 Remarkably, is enhanced by a factor ∼44 in the gap between nanospheres, compared to the incident plane wave. This enhancement reaches ∼75 times for the fixed incident direction along k x k y .…”

“…Our simulations are performed using a rigorous solution of Maxwell's equations for multi-particle clusters, the superposition T-matrix method. 40,[44][45][46] In this framework, incident and scattered fields are expressed in bases of vector spherical waves; the scattering properties of the cluster are thereby captured in a way that is independent of the incident field, leading to efficient calculations for multiple independent incident fields, and to analytical formulas for orientation-averaged properties. These provide accurate benchmark results against which the performance of numerical methods can be tested.…”