Jussi Behrndt, Hagen Neidhardt, Joachim Rehberg Block operator matrices, optical potentials, trace class perturbations and scattering (292K, Postscript) ABSTRACT. For an operator-valued block-matrix model, which is called in quantum physics a Feshbach decomposition, a scattering theory is considered. Under trace class perturbation the channel scattering matrices are calculated. Using Feshbach's optical potential it is shown that for a given spectral parameter the channel scattering matrices can be recovered either from a dissipative or from a Lax-Phillips scattering theory.