In industry, a large number of mechanical pieces need a specific treatment in order to improve their behavior towards aggressions such as erosion, corrosion, fatigue and high temperature. These treatments consist in transformation hardening, surface melting, surface alloying or surface cladding. High power continuous-wave C02 laser has been pointed out as one of the most attractive way to carry out such surface treatments.With respect to other conventional ones, this method has got many advantages such as energy transport without any material support, adaptable beam shaping, precise localization of the energy deposit, very thin thermal affected zone, etc... In this paper, surface melting of cast irons and of 304 L stainless steel are principally studied. The case of cast iron surface melting is of great interest because of the widespread use of this material in industry. In particular, in automotive industry, cast iron has been used for the manufacturing of camshafts, diesel motor cylinders, etc In the case of surface melting, the liquid region may be the seat of very important motions due to high temperature gradients at the surface of the melted pool. This convection has a great influence on the final structure of the thin treated layer of the metal specimens. In order to improve our knowledge on laser-material interaction, a new method for the visualization of the melt geometry and of the melt dynamics is necessary. This method involves an analysis of the temporal stability of the melted pool and velocity measurements of solid particles at the surface of the bath as well. The thermal field at the surface of the pool is also obtained by means of an optical method. In the first part, a brief overview of the main physical processes which take place during laser-matter interaction is presented. In the second part, the experimental set-up is described, and then, the first results are analyzed in the last part of the report.