  The optical properties of nanoparticle clusters vary with the spatial
arrangement of the constituent particles, but also the overall orientation of
the cluster with respect to the incident light. This is particularly important
in the context of nanoscale chirality and associated chiroptical responses,
such as circular dichroism or differential scattering of circularly polarised
light in the far-field, or local degree of optical chirality in the near-field.
We explore the angular dependence of such quantities for a few archetypal
geometries: a dimer of gold nanorods, a helix of gold nanospheres, and a linear
chain of silicon particles. The examples serve to illustrate the possible
variation of chiroptical responses with the direction of light's incidence, but
also, consequently, the importance of a robust orientation-averaging procedure
when modelling general clusters of particles in random orientation. Our results
are obtained with the rigorous superposition T-matrix method, which provides
analytical formulas for exact orientation-averaged properties.
