Evaluation of the role of beam homogeneity on the mechanical coupling of laser-ablation-generated impulse

The material emitted from a target surface during laser ablation generates a net thrust (propulsion) in the opposite direction. The momentum generation efficiency of this laser-driven propulsion is given by the mechanical coupling coefficient (Cm). In this work, we considered nanosecond UV laser ablation of the aluminum 6061 alloy to study the Cm behavior with different irradiating conditions. This is done by systematically changing fluence, uniform/nonuniform intensity, and incident angle of the laser beam. In particular, we found that when dealing with nonuniform laser intensity, characterizing Cm exclusively in terms of fluence is not fully satisfactory because the energy distribution over the irradiated area plays a key role in the way material is removed—interplay between vaporization and phase explosion—and thrust is generated.