Theory of Free-Carrier Absorption in n-PbSe l) J. S Z Y M A~S K IFree-carrier absorption is calculated for n-type PbSe using the model of a nonparabolic, nonspherical, and multivalley conduction band. New scattering mechanisms of the electron in PbSe-like structure (two-band deformation potential for optical phonons and twooptical-phonon deformation potential) are considered in order t o explain the recent experimental data on n-PbSe.L'absorption par les porteurs libres est calcul6e pour n-PbSe utilisant le modele de la bande de conduction Zt plusieurs vallbes nonspheriques et nonparaboliques. Ppur expliquer les exphriences pour n-PbSe on considhe des nouveaux processus de diffusion des porteurs libres diis aux interactions nonpolaires des 6lectrons avec les phonons optiques. l) This work was supported by the Institute of Physics of the Polish Academy of Sciences. a) Of course, t(w) does not depend, by definition, on the electron energy and exists even if the relaxation time approximation for Boltzmann equation does not hold.