Ignition. by laser diode, of explosive reactions on pyrotechnical mixtures is presented in this paper. A model was studied in order to determine the ignition threshold energy of the pyrotechnic compositions. It results in a numerical solution of the heat equation, in transient, with a source term due to the in-depth absorption of the laser radiation. The chemical reaction is modelled by the way of a kinetic law based upon an Arrhenius law. In order to take into account this interface phenomenon, a thermal resistance R-c of contact was introduced at the interface sapphire windows-pellet. In this article, we propose to optimize this term and the depth mu of absorption of the laser radiation, in order to minimize the deviation from the experimental results. We thus obtain the value of R-c and of mu. While varying various parameters (density of power, porosity, percentage of carbon black), the adequacy of calculations and the experimental results will be highlighted. Based on the results obtained we show in Fe/KClO4 mixture that the energy threshold is controlled more particularly by the conditions of the interface represented by the thermal resistance of contact R, and coefficient of absorption mu.