ORIGIN OF LIGHT-SCATTERING FROM DISORDERED-SYSTEMS

Anelastic light scattering is computed numerically fur model disordere d systems (linear chains and 2-dimensional site and bond percolators), with and without electrical disorder, A detailed analysis of the vibr ational modes and of their Raman activity evidences that two extreme m echanisms for scattering may be singled out. One of these resembles sc attering from finite size systems, while the other mechanisms originat e from spatial fluctuations of the polarizability and is such that mod es in even small frequency intervals may have very different Raman act ivities. As a consequence, the average coupling coefficient C(omega) i s the variance of a zero-average quantity, Our analysis shows that for both linear chains and 2-dimensional percolators the second mechanism dominates over the first, and therefore Raman scattering from disorde red systems is essentially due to spatial fluctuations.