Measuring the quasi-universality properties of wavelength-scale scatterers.

Some peculiar quasi-universality properties and patterns in light scattering by particles in the intermediate size range have been the subject of several recent theoretical studies, with a particular focus on dielectric spheres. We report experimental evidence of such behaviour by measuring the forward scattered intensity by size-polydisperse water droplets suspended in air, as well as oil-in-water emulsions, and independently deducing their refractive index, hence the internal coupling parameter for each particle. Moreover, we find deviations from the quasi-universality behaviour of spheres for non-spherical objects, especially when size is close to the wavelength of light. We expect that these properties help refine sizing and characterization of particles in the critical micrometric size range spanned by aerosol particles most relevant to radiative transfer.