Abstract: The femtosecond laser can be used for the precise machining of explosives and the preparation of energetic nanomaterials because of its ultra-short pulse duration and ultra-high energy density. Deep understanding of the femtosecond laser ablation mechanism of energetic materials is the basis for rational use of femtosecond laser machining technology. The molecular dynamics calculations of RDX ablated by femtosecond laser were conducted based on ReaxFF/lg reactive force field. The decomposition reaction pathway and particle diffusion of RDX were analyzed, and the ablation mechanism of RDX under different femtosecond laser energies was discussed. Results show that the ablation mechanisms of RDX are different under the action of different femtosecond laser energies. When the laser energy is high enough (e.g., 1.0 mJ/pulse, 51 J/cm²), RDX is rapidly decomposed to generate high-temperature and high-pressure plasma. In addition, there are many single atoms, ions and small molecular fragments in the products; when the laser energy is relatively low (e.g., 0.2 mJ/pulse, 10.2 J/cm²), the explosive is removed by a photomechanical ablation mechanism, RDX in laser focal zone escapes as its starting molecular structure. During the femtosecond laser ablation, the high-speed particles in focal zone quickly escape outward and become difficult to transfer the energy to the surroundings, by which the explosive can be removed effectively without causing thermal diffusion. Therefore, the “cold” machining of explosives can be realized.

Key words: RDX, moleculardynamics, femtosecondlaser, ReaxFF/lg