Femtosecond laser pulse-train induced breakdown in fused silica: the role of seed electrons
Femtosecond laser pulse-train induced breakdown in fused silica: the role of seed electrons
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DOI：
10.1088/0022-3727/47/43/435105
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发表时间：
2014-10
期刊：
影响因子：
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通讯作者：
Kaihu Zhang;Lan Jiang;Xin Li;Xuesong Shi;D. Yu;L. Qu;Y. Lu
中科院分区：
文献类型：
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作者：
Kaihu Zhang;Lan Jiang;Xin Li;Xuesong Shi;D. Yu;L. Qu;Y. Lu
从理论上研究了飞秒激光脉冲串在熔融二氧化硅中的击穿，重点研究了超快种子电子在脉冲串激发过程中的作用。材料击穿阈值由激发模型和包含自陷态激子(STE)光吸收的改进光学模型组成。结果表明，单串诱导击穿阈值的演化是由引发电子雪崩的三个相互竞争的种子电子源的相互作用决定的：前一个脉冲留下的剩余导带电子、致密介质中原子的光致电离和后续脉冲对STE的光电离。第三个源为理解所涉及的一些潜在和现有问题提供了关键，并在脉冲串处理成为主导时导致许多与脉冲分离无关的现象(例如表面损伤/烧蚀大小)，并有助于可重复处理。对于两个或几个飞秒脉冲的单个序列，只有当第一脉冲能量超过一个临界值，即单脉冲击穿阈值的~65%-75%时，第三源才能在大脉冲间隔下占据主导地位并保持下去。计算结果与实验数据吻合较好。
Femtosecond laser pulse-train induced breakdown in fused silica is investigated theoretically, with a focus on the role of ultrafast seed electrons during the pulse-train excitation. Material breakdown threshold is investigated by a model, which consists of both the excitation model and an improved optical model by including the optical absorption of self-trapped excitons (STEs). It is found that the evolution of a single train induced breakdown threshold is governed by the interplay of three competing sources of seed electrons initiating an electronic avalanche: residual conduction-band electrons left by the previous pulse, photoionization of atoms in dense media and photoionization of STEs by subsequent pulses. The third source provides a key to the understanding of some potential and existing problems involved, and leads to many pulse-separation independent phenomena (e.g. surface damage/ablation size) for pulse-train processing when it becomes dominant, and can contribute to the repeatable processing. For a single train of two or several femtosecond pulses, the third source can become dominant and sustained at large pulse-separations only when the first-pulse energy is over a critical value, ~65–75% of the single-pulse breakdown threshold. Our calculations are in agreement with the experimental data.