  Many experimental systems consist of large ensembles of uncoupled or weakly
interacting elements operating as a single whole; this is the case in many
experimental systems in nano-optics and plasmonics including colloidal
solutions, plasmonic nanoparticles, dielectric resonators, antenna arrays, and
others. In such experiments, measurements of the optical spectra of ensembles
will differ from measurements of the independent elements even if these
elements are designed to be identical as a result of small variations from
element to element, known as polydispersity. In particular, sharp spectral
features arising from narrow-band resonances will tend to appear broader and
can even be washed out completely. Here, we explore this effect of
inhomogeneous broadening as it occurs in colloidal nano-polymers comprising
self-assembled nanorod chains in solution. Using a technique combining
finite-difference time-domain (FDTD) simulations and Monte-Carlo sampling, we
predict the inhomogeneously-broadened optical spectra of these colloidal
nano-polymers, and observe significant qualitative differences compared to the
unbroadened spectra. The approach combining an electromagnetic simulation
technique with Monte-Carlo sampling is widely applicable for quantifying the
effects of inhomogeneous broadening in a variety of physical systems, including
those with many degrees of freedom which are otherwise computationally
intractable.
