Impulse generation by confined laser ablation: polymers and thin films

Due to the high velocities of the ejected material during laser ablation, a measurable mechanical impulse is generated on the irradiated material, so this technique has gained interest as a possible space propulsion technique. This possibility became increasingly attractive with the advent of large constellations of nanosatellites and with the emerging problem of space debris mitigation, since both these applications require to control far objects that can not bring on board a propulsion system. To make laser ablation propulsion(LAP) applicable to nanosatellite propulsion, it is fundamental to understand the processes involved in the impulse generation process, in order to develop optimized target materials for this application. To this aim, the optical coupling of the material with the laser can be optimized, while a consistent enhancement of the generated impulse can be obtained by confining the expansion of the ablation plume using a transparent layer. Confined laser ablation can therefore be a possible solution for nanosatellite propulsion. Using a specifically designed ballistic pendulum to measure laser generated impulse, confined ablation was studied in the case of thin confinement layers and composite polymeric materials. Investigation of systems with thin confinement layers allowed to highlight some general features and the main problems of the impulse generation process exploiting this kind of geometry. On the other hand, results on composite polymers show that it is possible to obtain structures in which the interaction with the laser pulse results in the spontaneous formation of a confinement layer, that opens the way to obtain confined ablation also with multiple pulses.