Dynamics characteristics of a laser-induced non-spherical bubble collapsing micro-jet and its enhancement on hard tissue ablation

• Mechanism of liquid-assisted laser ablation of in vitro hard tissue was analyzed. • Normalized distance γ affects dynamics of laser-induced aspherical cavitation. • Micro-jet impact is main cause of bone ablation during hemispherical cavitation. • Effects of micro-jet vectors on bone ablation pits are quantitatively analyzed. • Ablation depth can be effectively controlled by adjusting normalized distance γ . Liquid-assisted laser ablation has been investigated in osteotomy and dentistry with the aim of removing tissue while minimizing thermal injury. In this paper, the dynamics of a laser-induced non-spherical bubble collapsing micro-jet vector as well as its scaling relationship with the output tissue ablation are described. The velocities of the micro-jets with normalized stand-off distances ( γ ) from 0.1 to 0.7 are determined in the range of 24–35 m/s, while the corresponding crater depths are in the range of 260–1020 µm with a diameter-to-depth ratio of 0.7 to 1.9. The results show that the geometrical characteristics of the incubation crater ablated in the bone are closely related to the micro-jet vector. The crater depth and diameter are positively dependent on the micro-jet velocity and micro-jet diameter, while crater's diameter-to-depth ratio is negatively correlated with the micro-jet velocity. The corresponding micro-jet impact strength on the bone tissue is about 85.2–123.5 MPa, with the micro-jet velocity ranging from 24 m/s to 35 m/s, and the impact pressure decreases rapidly along the central axis outward, resulting in the U-shaped ablation crater. The results show that adjusting γ is an effective method for controlling the micro-jet vector and the resultant bone ablation.