Determining degree of scattering in structurally-colored colloidal glasses*

The reflection spectra produced by colloidal glasses comes from both single and multiple scattering. Interference between the waves scattered from these structures results in reflection peaks that we perceive as colors, termed structural colors because they come from the nanoscale structure rather than from absorption. While the location of the primary structural resonance can be predicted using a single-scattering theory, other features of the spectrum, such as the increase in reflection at small wavelengths, cannot be explained by single scattering alone. To experimentally measure how much light is multiply-scattered in these systems, we detect light reflected from colloidal glasses through crossed polarizers, which only pass light that has been scattered more than once. To extract the degree of multiple scattering, we use a Monte Carlo approach to simulate photons traveling through the glass, tracking the number of scattering events before photons exit the sample. By fitting the model to the experimental data, we can gain new insight into how the degree of scattering affects the off-resonant features of the reflectance spectra of colloidal glasses.