SYMMETRY-RELATIONS FOR FORWARD AND BACKWARD SCATTERING BY RANDOMLY ORIENTED PARTICLES

Symmetry considerations are used to derive relations for scattering of light in the exact forward and backward directions. It is shown that in some cases simple relations for the non-diagonal elements of the am plitude matrix yield simple linear equations for the diagonal elements of the scattering matrix, both for one particle and collections of pa rticles. Special attention is given to particles having at least one p lane of symmetry and to rotationally symmetric particles, both in rand om orientation. Properties of the scattering matrices of collections o f randomly oriented particles for the forward and backward directions are summarized in two tables. To confirm the theoretical relationships and to gain more insight in their domains of validity, the special ca ses of very small and very large particles were considered and numeric al experiments were conducted, using the T-matrix approach. Some resul ts of these experiments for regular tetrahedra and straight chains of four identical spheres are presented. (C) 1998 Elsevier Science Ltd. A ll rights reserved.