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High-power laser cutting with oxygen as assisting gas is used extensively in industry, but requires optimisation of a large number of process variables to obtain a good cut quality. These values depend largely on the absorption of the laser beam by the work piece material and therefore on the wavelength of the laser used, but also of the surface state of this material. In order to specify the proportion absorbed for various states of the surface in laser cutting, an experimental determination of the absorbivity of a carbon steel with different degrees of surface oxidation has been undertaken. The measurements carried out during cutting enable the various energy contributions to be evaluated: that provided by the laser and the oxidation reactions, that used to melt and eject the molten metal, and that diffused in the part cut out. Numerical modelling of cutting, using experimental measurements of the various energies in the CFD software Fluent, enables an analysis to be made of physical mechanisms involved in the ejection of the molten pool. [ABSTRACT FROM AUTHOR]