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157nm激光刻蚀晶体光纤SiO2机理的研究
Mechanism study of silica ablating on photonic crystal fiber by 157 nm laser
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摘要: 为了研究157nm激光对SiO2材料的加工特性,用157nm激光刻蚀晶体光纤的端面,以晶体光纤的微孔轮廓作为参照,对刻蚀深度和烧蚀程度进行定量地分析。157nm激光的光子能量达7.9 eV,能够被SiO2强烈地吸收,会在SiO2上诱导出点缺陷结构,产生大量的种子电子。同时光纤SiO2材料的掺杂使157nm激光损伤的阈值大大降低,实际加工速率达210nm/脉冲。结果表明,由于单光子雪崩电离吸收的速率远高于高阶多光子吸收的速率,所以157nm激光对SiO2材料损伤的主要机理是单光子雪崩电离吸收过程,破坏其分别占一半的离子键和共价键。在刻蚀过程中会产生热量,但由于损伤产生的时间仅20ns,形成的热影响区很小,故可得到较高的加工质量。Abstract: To test 157nm silica ablating effect,the profile of micro holes on the end cross section of silica photonic crystal fiber is employed under the exposure of 157nm laser to quantitatively analyze the ablating depth and degree.The photon energy of 157nm laser is 7.9eV,can be absorbed by silica.Under 157nm laser,the defect formations in silica are accumulated to produce a large quantity of free electrons.Meanwhile,the dopants in fiber silica considerably reduce the breakdown threshold.Because the rate of single-photon absorption outclasses the rate of multi-photon absorption,it can be inferred that the mechanism of interaction between 157nm laser and silica is a process of single-photon absorption of electron-avalanche.It breaks all bonds in silica,a half of them is ionic bonds and the other half is covalent bonds.The actual ablating velocity 210nm/pulse has demonstrated that the 157nm laser can be absorbed strongly by silica material and that thermal process accompanies with the ablation,however,because the period of damage is only 20ns,the heat on the silica can be limited in a extremely small area,therefore,an ablating result with good quality can be ensured.
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Key words:
- laser technique /
- SiO2 /
- ablation /
- photonic crystal fiber
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