Study on the mechanism of 355 nm laser ablation of hard bone tissue mediated by annular water mist

Laser ablation is a promising approach for processing hard bone tissue; however, maintaining ablation performance while minimizing thermal injury remains challenging. This study proposes annular water mist-mediated 355 nm laser ablation, in which a central air channel provides a relatively dry optical path for laser transmission, while the surrounding water mist removes heat from the interaction region. A qualitative finite-element thermal model and ablation experiments were used to compare four cooling conditions: no cooling, surface water-film-assisted cooling, paraxial water-mist-assisted cooling, and coaxial annular water-mist-assisted cooling. The influences of nozzle height, water flow rate, and air pressure in coaxial annular water-mist-assisted cooling on groove depth, groove width, and the heat-affected zone were further investigated. The results show that annular water mist maintains a relatively high ablation depth while markedly reducing thermal damage and surface crystalline-layer formation. Thus, the proposed approach provides an effective balance between ablation depth and thermal-damage suppression during 355 nm laser processing of hard bone tissue.