The complexity of the phenomena simultaneously occurring, from the very first instants of high-power laser pulse interaction with the target up to the phase explosion, along with the strong changes in chemical-physical properties of matter, makes modeling laser ablation a hard task, especially near the thermodynamic critical regime. In this work, we report a computational model of an aluminum target irradiated in vacuum by a gaussian-shaped pulse of 20 $\mathrm{n}$$\mathrm{s}$ duration, with a peak intensity of the order of $\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}{}^2$. This continuum model covers laser energy deposition and temperature evolution in the irradiated target, along with the mass removal mechanism involved, and the vaporized material expansion. Aluminum was considered to be a case study due to the vast literature on the temperature dependence of its thermodynamic, optical, and transport properties that were used to estimate time-dependent values of surface-vapor quantities (vapor pressure, vapor density, vapor and surface temperature) and vapor gas-dynamical quantities (density, velocity, pressure) as it expands into vacuum. Very favorable agreement is reported with experimental data regarding: mass removal and crater depth due to vaporization, generated recoil momentum, and vapor flow velocity expansion.

The continuously growing number of micro and nanosatellites launched in recent years has stimulated research institutes and industries to find alternative and less expensive ways to reach Low Earth Orbits. Laser ablation propulsion is one of the most promising launching techniques, even though a dedicated and reliable testing system has not been discussed in literature. We present a simple and dependable apparatus for measurements of laser ablation generated impulse and ejected mass. Impulse measurements are performed by using a ballistic pendulum, specifically designed for µ N s impulses, whose oscillations are accurately detected by means of a reflected probe laser with a long optical path, which leads to a measurement accuracy of around 1%. The apparatus provides fast and reliable measurements that take into account the variability in centre of mass and moment of inertia that occur by changing the target material on the pendulum. Ablated mass measurements exploit the programmable displacements of a dedicated target irradiated with a large number of laser shots to increase the resolution of the measurement. The apparatus is tested with a KrF excimer laser at 248 nm and pulse width of 20 ns onto an aluminum target: a highly reproducible series of measurements of momentum coupling coefficient ( C m ) with a standard deviation of around 1% is presented, along with a specific impulse ( I s p ) in favourable accordance with the literature.

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 ( C m ). In this work, we considered nanosecond UV laser ablation of the aluminum 6061 alloy to study the C m 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 C m 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.