  Spatial interferometry, based on the measurement of total absorbed power, can
be used to determine the state of coherence of the electromagnetic field to
which any energy-absorbing structure is sensitive. The measured coherence
tensor can be diagonalized to give the amplitude, phase, polarization patterns,
and responsivities of the individual electromagnetic modes through which the
structure can absorb energy. Because the electromagnetic modes are intimately
related to dynamical modes of the system, information about collective
excitations can be found. We present simulations, based on the Discrete Dipole
Approximation (DDA), showing how the dynamical modes of systems of surface
dipoles can be recovered. Interactions are taken into consideration, leading to
long-range coherent phenomena, which are revealed by the method. The use of DDA
enables the interferometric response of a wide variety of objects to be
modeled, from patterned photonic films to biological macromolecules.
