Enhancement of Raman Cross Section in CdS due to Resonant Absorption

We have observed marked resonant enhancement of the Raman cross section for phonons in CdS at frequencies near the absorption edge. The data, taken at 77\ifmmode^\circ\else\textdegree\fi{}K, can be explained on the basis of a simplified model in which the absorption band is replaced by a single effective frequency coinciding with the band edge to within one percent. The experimental technique involved collecting Raman radiation scattered from the surface of the crystal.