Time resolved study of the laser ablation induced shockwave

Laser ablation is used in laser plasma thrusters (LPT), in which the created plasma provides the thrust that is used to stabilize the trajectory of satellites in space. To allow the use of IR laser diodes, an IR absorber has to be added to the polymer. As a measure of the energy released during ablation of such polymers, the shockwave velocity in air is measured with shadowgraphy. The measured shockwave velocities of a cross-linked glyzidyl azide polymer (GAP) incorporating carbon particles (as broad range absorber), reveal that the shockwave velocity decreases with the increasing irradiation wavelength (193-1064 nm) for a given fluence. In addition, the shadowgraph images reveal that for irradiation with shorter wavelengths, the amount of solid fragments decreases and more gaseous products are released. Comparing the shockwave propagation of GAP and a triazene polymer reveals that both polymers exhibit similar shockwave velocities at UV irradiation wavelength, whereas with 1064 nm irradiation, the shockwaves generated using GAP propagate faster. These results are probably due to the change of the absorption site, the mechanism of ablation, and the different decomposition enthalpies