Orientational averaging of integrated cross sections in the discrete dipole method

Using the discrete dipole method, exact and approximate analytical solution s for orientation-averaged cross sections for extinction, absorption, and s cattering of light are obtained. The analytical solutions can be applied to the calculation of integrated cross sections of fractal clusters formed by primary particles with different optical properties (soot in air and aqueo us suspensions of aggregates of polystyrene, gold, and silver nanoparticles ). It is shown that two models of aggregates that differ only in trajectori es (ballistic or Brownian) of primary particles and intermediate clusters a nd in average fractal dimensions give close values of averaged extinction c ross sections. (C) 2001 MAIK "Nauka/Interperiodica".