The role of beam homogeneity in mechanical coupling evaluation of laser ablation-generated impulse

TL;DR

This study investigates how laser beam uniformity affects the mechanical coupling coefficient in laser ablation of aluminum, revealing that beam homogeneity significantly influences propulsion efficiency and material removal mechanisms.

Contribution

It introduces an analysis of beam homogeneity effects on Cm during nanosecond UV laser ablation, highlighting the importance of energy distribution over fluence alone.

Findings

Beam nonuniformity impacts Cm measurement accuracy.

Energy distribution influences vaporization and phase-explosion dynamics.

Uniform beams yield more predictable propulsion performance.

Abstract

The material emitted from the target surface during laser ablation generates a net thrust (propulsion) in the opposite direction. The energetic 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 behaviour 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.