An approximate method for calculating scattering and absorption of light by fractal aggregates

A simplified version of the coupled dipole method (CDM) is proposed which a llows one to reduce the initial system of 3N x 3N equations to a simpler sy stem of N x N equations. The method neglects depolarization effects in the interaction of dipoles but, unlike the mean field approximation, it takes i nto account local fluctuations of the scalar amplitudes of the excited dipo le moments. Simple analytic solutions are obtained for integrated cross sec tions averaged over aggregate orientations. It is shown by the example of b allistic fractal aggregates that this method provides the accuracy close to that of a standard CDM, being substantially less time-consuming. In the ca se of biospheres, the approximate method is compared with the exact results of the multipole expansion. (C) 2000 MAIK "Nauka/Interperiodica".