Theory of Resonant Raman Scattering in Crystals: A Generalized Bare-Exciton Approach

Abstract

The bare-exciton theory of light scattering in crystals is generalized to include dispersive effects, and to incorporate damping in a first-principles calculation. The theory is applied to exciton-mediated Raman scattering; expressions for the first- and second-order Raman cross sections due to a single discrete exciton level are derived, and the resonance behavior investigated. For small couplings and intermediate dampings the predictions of the present generalized theory are very similar to available bare-exciton and undamped-polariton predictions, while differing, however, for large couplings. The cross sections are resonant when the incoming or outgoing photon frequencies lie near an exciton frequency, and peak sharply for small photon-exciton couplings and dampings. Actual calculations are presented for various choices of the parameters, among them parameters appropriate to CdS. A comparison of the present theory with other theories and with experiment is carried out.