Mechanism of femtosecond laser ablating NiTi shape memory alloy
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摘要: 结合双温模型的分子动力学模拟方法，研究了飞秒激光脉冲辐照B2结构镍钛合金时烧蚀阈值附近的靶材蚀除机制，数值模拟了中心波长为800 nm，脉宽为100 fs，能量密度为25~50 mJ/cm2的激光与90 nm厚B2结构镍钛合金薄膜相互作用过程。确定了脉宽为100 fs的脉冲激光与镍钛形状记忆合金相互作用的烧蚀阈值，发现烧蚀阈值条件下，靶材的蚀除机制是单纯基于应力作用的机械破碎；烧蚀阈值附近，未蚀除靶材受热影响发生无序化相变的区域较小，且随激光能量密度的降低而减小。 提高激光功率密度，烧蚀同时呈现热机械蚀除和机械破碎机制。Abstract: The mechanism of femtosecond(fs) laser ablating B2 NiTi alloy have been investigated by the molecular dynamic simulations combined with the two-temperature model. A series of simulations have been conducted, in which ,the laser used is 800 nm in central wavelength, 100 fs in pulse duration, and from 25 mJ/cm2 to 50 mJ/cm2 at fluence. The target is 90 nm in depth. The fluence threshold for 100 fs pulsed laser ablating NiTi shape memory alloy is determined, and it is found that the target irradiated by threshold fluence is ablated wholly due to the tensile and the heat induced phase change area is the smallest. When the fluence is improved, the phase change area expanded.
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