Abstract
Transmission and reflectivity measurements on thin epitaxial samples of Pb1-xMnxTe (x<or=0.02) are analysed in the vicinity of the absorption edge using a novel numerical procedure which takes full account of internal interference and dispersion. The spectral dependence of the absorption coefficient is well described by a two-band k.p model. The resulting energy gap increases by up to 40% for x=2% at low temperatures as compared to PbTe. From far infrared investigations, no significant influence of x is found on the lattice dynamical properties.