Modification of the temporal laser source term in two-temperature model

Simulations on the interaction between laser pulses with materials during pulsed laser ablation require information on the characteristics of both laser and material. While details on material properties are extensively studied, the temporal profile of the laser source term is rarely studied and is generally assumed to be Gaussian. This article explores the effects of non-Gaussian temporal laser source terms (TLSTs) in simulating the heat diffusion within a metal upon irradiation of femtosecond pulsed lasers. We employed the Two-Temperature Model (TTM) to simulate the temperature evolution on the surface of copper upon irradiation of a 100-fs laser pulse with different TLSTs at different laser repetition modes (single-shot, burst, and biburst). We used a constant total fluence of 3J/cm ² in all cases and subsequently calculated the ablation depths based on the resulting temperature values. Our results show that non-Gaussian TLSTs generate lower electron and lattice temperatures, resulting in shallower crater depths compared to a Gaussian TLST. However, under burst and biburst modes, particularly with higher subpulse number repetition time, the results of non-Gaussian TLSTs approximate those of Gaussian TLSTs. To initiate laser ablation in such cases, higher laser fluence might be required. Our work on non-Gaussian temporal profiles in TTM simulations can be applied to other computational methods in describing laser-matter interaction.脉冲激光烧蚀过程中激光脉冲与材料相互作用的模拟，需要同时获取激光与材料两方面的特性参数。尽管学界已对材料属性开展了大量深入研究，但激光源项的时间轮廓却鲜有探讨，且通常被默认设定为高斯型分布。本文探讨了非高斯时间域激光源项（non-Gaussian temporal laser source terms, TLSTs）对飞秒脉冲激光辐照下金属内部热扩散模拟的影响。我们采用双温度模型（Two-Temperature Model, TTM），针对不同激光重复模式（单脉冲、脉冲串及双脉冲串）下、总激光能量密度（fluence）固定为3 J/cm²的100飞秒激光脉冲，模拟了不同TLSTs辐照铜表面时的温度演化过程，并基于所得温度值计算了烧蚀深度。结果表明，相较于高斯型TLSTs，非高斯型TLSTs会产生更低的电子与晶格温度，进而导致更浅的烧蚀坑深度。然而在脉冲串与双脉冲串模式下，尤其是当子脉冲数量更多、重复周期更短时，非高斯型TLSTs的模拟结果会逐渐趋近于高斯型TLSTs的结果。此时若要启动激光烧蚀过程，可能需要更高的激光能量密度。本文针对双温度模型中采用非高斯时间域轮廓的相关研究，可推广应用于其他描述激光-物质相互作用的计算方法中。