A method using lasers of segregation of impurities or interstitial mercury atoms (IMA) in solid phase Hg0.8Cd0.2Te (MCT) is presented. A theoretical model for this process is also proposed. The equation for the diffusion of impurities or IMA was completed by a term describing the influence of phonon flux on diffusion processes. Computer simulations of the laser annealing process reveal the possibility of obtaining a sharp maximum of Hg concentration for appropriately chosen parameters of laser pulse. This was verified experimentally with MCT specimens annealed by using a YAG:Nd3+ laser.