  Light-scattering in the terahertz region is demonstrated for granular matter.
A quantum-cascade laser is used in a benchtop setup to determine the
angle-dependent scattering of spherical grains as well as coffee powder and
sugar grains. For the interpretation of the form factors for the scattering
from single particles one has to go beyond the usual Rayleigh-Gans-Debye theory
and apply calculations within Mie theory. In addition to single scattering also
collective correlations can be identified and extracted as a static structure
factor.
