短脉冲激光加工双温方程的优化运算

Calculation of An Optimized Two Temperature Model for Ultra-short Laser Ablation

为研究双温方程中电子热传导项和电子与晶格耦合项对激光辐照物体表面温度场求解的影响,对这两项施加了约束条件。由于飞秒和亚皮秒激光与物质相互作用时间短,电子与晶格来不及耦合,所以对耦合项施加时间约束;根据相分离条件(CPPS),对热传导项施加空间约束。利用有限元方法建立了激光烧蚀金属铜膜表面的有限元模型。通过分析双温方程中热传导项和耦合项对计算结果的影响,发现短脉冲激光与铜金属相互作用过程中电子与晶格耦合项可以忽略,而传导项不可忽略。求解适当激光功率下的双温方程,得到了激光作用中心电子与晶格在不同脉冲宽度激光辐照下的温度变化关系。根据100 fs激光作用后晶格温度场的空间分布情况,研究了激光作用的相分离区域、相爆炸区域以及熔融区域的分布情况。

Since the pulse duration of femtosecond and sub-picosecond laser are quite short,the electrons and lattice in material can＇t couple in time when the sample is irradiated by ultra-short pulse laser.According to critical-point phase separation（CPPS） theory and actual laser ablation process,the thermal conductivity in the model can be restricted regionally.Based on aforementioned analysis,an optimized two temperature model（TTM） is formulated,which provides a new perspective into the energy transport process during ultrashort single pulse laser ablation.Using finite element analysis（FEA） software,a model which exhibits the cuprum film sample irradiated by ultrashort pulse laser is proposed.Taking account of symmetrical spatial shape of Gaussian distribution laser on the sample,part of the model is used to calculate simply.According to calculation,the electron-lattice coupling and thermal conduction transient parts in the optimized TTM are analyzed separately.The results indicate that,during ultra-short laser irradiating on cuprum film,the coupling item can be neglected,but the conduction item can＇t be neglected.The conduction item plays a major role during femtosecond and sub-picosecond laser irradiating on cuprum,while the electron-lattice coupling item plays a major part after laser＇s effect.With finite element method（FEM）,the optimized 1D and 2D TTM model are calculated.For the purpose of ablating sample,suitable laser pulse fluence of 100 fs,300 fs,1 ps,2 ps are applied.The electron and lattice transient temperature distribution evolutions along time in the centre of laser irradiated zone are obtained.For further analysis,according to the spatial lattice temperature distribution,phase separation zone,phase explosion zone and melting zone are calculated.