Effects of optical absorption on the main resonance in light scattering by acoustic modes in superlattices

A dynamical theory of backscattering of light off the acoustic longitudinal field of a two-component (GaAs-Ga 1-x Al x As) superlattice is discussed. It is first shown that when the opacity of the sample is ignored the theory predicts one main peak due to the lowest Bloch pole plus other weaker resonances due to the higher Bloch poles. When the opacity of the superlattice is included in the theory the spectrum contains additional contributions from bulk-type resonances. These are manifest in the shape of the main peak and appear as shoulders asymmetrically superimposed on the main resonance at the lowest Bloch pole. This is a prediction of the theory which deserves experimental study. Illustrations are given for the case of light from an argon ion laser at 5145 AA incident on a GaAs-Ga 0.6 Al 0.4 As superlattice of equal layer thicknesses d 1 =d 2 =100 AA.