We examine experimentally the modifications induced at the surface of silicon and IV-IV alloys by an excimer laser above the melting threshold fluence. Laser irradiation takes place under vacuum, or in the presence of a gas. The resulting processes are respectively: laser induced polarization, pulsed laser induced epitaxy, incorporation of atoms from the gas phase, and laser chemical etching. In turn, the laser induced surface modifications and the presence of adsorbates on the surface cause important changes in the melting/solidification cycle. We describe a model calculation which takes into account non-equilibrium heat diffusion, phase change, atom diffusion, segregation and desorption. The model is applied to the laser chemical etching process, and its results are compared to the experimental data. This simulation brings information on the segregation of chlorine and on the dynamics of desorption.