Femtosecond laser pulse-train induced breakdown in fused silica: The role of seed electrons

Kaihu Zhang, Lan Jiang, Xin Li, Xuesong Shi, Dong Yu, Liangti Qu, Yongfeng Lu

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Abstract

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.

Original languageEnglish (US)
Article number435105
JournalJournal of Physics D: Applied Physics
Volume47
Issue number43
DOIs
Publication statusPublished - Oct 29 2014

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Keywords

  • laser materials processing
  • laser-induced breakdown
  • pulse train
  • seed electrons

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Acoustics and Ultrasonics
  • Surfaces, Coatings and Films

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