The excimer laser nitriding process reported is developed to enhance mechanical properties of aluminum alloys. An excimer laser beam is focused onto the alloy surface in a cell containing 1 bar nitrogen gas. A vapor plasma is expanding from the surface and shock wave dissociates and ionizes nitrogen. Then vapor and gas species stay several hundreds of microsecond(s) in contact with the surface and nitrogen diffuses in depth. Thus it is necessary to work with a sufficient laser fluence to create the plasma, but this fluence must be limited to prevent from a too large laser-induced surface roughness. The nitrogen concentration profiles are determined from RBS and SEM coupled to EDX probe analysis. The roughness and surface state are studied to define the best irradiation conditions corresponding to a smooth and homogeneous surface.