Confined geometry and laser energy affect laser plasma propulsion

The interaction of plasma (or shock waves) with the uniform sphere shape of polystyrene particles was investigated in this study to observe the effects of confined geometry and energy fluence on propulsion efficiency. The measurements indicate that propulsion efficiency first increases with energy fluence until reaching a maximum at 0.46 J/cm², then decreases as energy fluency continues to increase. Compared to polystyrene particle propulsion without confined geometry, the propulsion efficiency of polystyrene particles improved due to multiple laser-induced shock wave reflections among the confined geometry internal face; the plasma propelling force also increased perpendicular to the target surface under confined geometry conditions. The results also show that the energy deposited on the plasma affects the energy distribution between the plasma and polystyrene particle. Moreover, a series of experiments was performed to roughly estimate the shock wave expansion shape through the motion direction of the polystyrene particle swarm, where the shock wave was observed to expand spherically.