CONTRIBUTION OF THE 2ND-ORDER BORN APPROXIMATION TO THE SCATTERED INTENSITY

Weak scattering is usually analyzed by using the first-order terms for the field to calculate the scattered intensity. We investigate the co ntribution to the scattered intensity made by the product of the zerot h-order and second-order terms of the Born approximation for the field , for two different geometries, for the case in which the scattering p otential is a zero-mean random process and the scattering medium is qu asi-homogeneous. It is shown that in some situations the product of fi rst-order terms is sufficient for calculating the scattered intensity, but that in other situations the contribution from the product of the zeroth-order and second-order terms must be included. This result is directly applicable to the question of whether spectral shifts will be observed in scattering from elastic media.