Two-phonon resonant brillouin scattering in CdS

We have identified the high frequency Brillouin peaks recently reported by Winterling and Koteles in CdS as due to scattering of two acoustic phonons. A theory of two-phonon resonant Brillouin scattering of polaritons is developed and found to reproduce well the position, linewidth and relative intensity of all the experimental peaks with only one adjustable parameter. By fitting the experimental peak positions the effective mass of the A exciton in CdS parallel to the c-axis is determined to be 2.7 ± 0.2 times the free electron mass. © 1978.