Optical response of saddle point excitons

The linear optical response of interband transitions near saddle points is studied within the framework of the effective mass approximation. The method is based on Stahl's configuration space theory. Unlike previous works the present treatment allows an unrestricted range of effective mass ratios, and it generates both real and imaginary part of the dielectric function. Spectra are calculated by numerical integration of a two dimensional second order partial differential equation. The results obtained for M₁ saddle points agree well with the observed lineshape of the E₁ peak in ZnTe.