Nanosecond laser irradiations were used to induce a dewetting process of a thin Au film on SiO2/Si. The melting and solidification dynamics of the film under the irradiations lead to a dewetting process whose driving force was identified in a Rayleigh instability mechanism. Such a mechanism determines the formation of Au nanoparticles from the melted quasi-continuous starting Au film. The mean nanoparticles size and spacing were quantified, finding their correlation as described by the surface-diffusion-limited Rayleigh instability theory.