飞秒激光多脉冲烧蚀过程中飞秒时间分辨电子状态的观测研究
Femtosecond Time-Resolved Electronic States in Femtosecond Laser Multipulse Ablation
查看参考文献18篇
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文摘
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为研究飞秒激光加工硬脆透明材料时存在的"微裂纹"与"诱导条纹"等共性工艺问题,利用飞秒时间分辨泵浦探测阴影成像技术,对飞秒激光多脉冲烧蚀石英玻璃过程中的电子动力学过程进行成像,分析了激光脉冲电离材料初期(700 fs之前)等离子体丝的演化情况。多脉冲诱导微结构的存在使成丝区域分布在微结构的两侧与光脉冲传播的轴线方向,前者主要是由微结构侧壁对光脉冲的折射造成的,而后者则是由微结构底面与侧壁形貌不同导致的光程差引起的。实验结果揭示了多脉冲加工过程中脉冲串诱导微结构对后续光场的重塑效应,该效应影响了等离子体成丝区域与能量沉积的分布,这是共性工艺问题产生的核心机制。 |
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其他语种文摘
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Objective This study investigates the prevalent process problems, such as "microcracking" and "induced streaking," in the femtosecond laser processing of hard and brittle transparent materials. The study employs the femtosecond time-resolved pump-probe shadow imaging technique to visualize the electron dynamics during the femtosecond laser multi-pulse ablation of quartz glass. Particularly, the plasma filament evolution at the early stage of laser pulse ionization(before 700 fs) is analyzed. The multi-pulseinduced microstructures distribute the filament formation regions on both sides of the microstructure with respect to the axial direction of the light pulse propagation. The distribution on both sides is primarily due to the refraction of the light pulse by the sidewalls of the microstructure, while that on the axis is caused by the difference in the shape of the bottom and sidewalls of the microstructure, creating the light range difference. The empirical results show that the pulse train induces a remodeling effect of the microstructure on the subsequent light field during multi-pulse processing, affecting the distribution of the plasma filament formation region and energy deposition-the core mechanism responsible for common process problems. Methods A femtosecond time-resolved pump-probe shadow imaging setup was built to capture the propagation and ionization process of a single subsequent pulse beneath the microstructure induced by irradiating the material with 219 fs pulses. First, the actual spatial location of the focus was determined by imaging the shadow of the air-ionized plasma at the focus. After that, the power density at the material surface was obtained for different focus positions. The distinctive" V" and" inverted trapezoid" shapes were obtained after controlling the relative positions of the laser focus and the material. Second, the ionization process of femtosecond timeresolved propagation of the 220th pulse under different microstructures was obtained by modulating the time delay between pump and probe beams. Finally, the ionized filament-forming regions in the transient ionization images were compared with the process defects to reveal the formation mechanism of the process defects. Results and Discussions The propagation and ionization process of the 220th pulse is observed using femtosecond time-resolved pump-probe shadow imaging(Figs. 5.6. 9.10). The physical mechanisms governing process problems such as "microcracking" in micromachining of hard and brittle materials are revealed. The light-field remodeling effect, guided by various morphology microstructures, leads to energy deposition and the mechanism of generating common process problems. In the context of multi-pulse processing, the influence of energy deposition(propagation and ionization) is determined by the linear refractive index of the material, a nonlinear refractive index that varies with the light intensity, plasma defocusing effect, microstructure morphology, and the focusing conditions in conjunction with the laser fluence on the material surface. Moreover, the relaxation time of ionized free electron number density during light field propagation is determined to be less than 300 fs across diverse microstructures. Conclusions Under multi-pulse irradiation, the remodeling effect of different microstructural morphologies on the subsequent light field orchestrates the nonlinear ionization process. In the case of the V-shaped structure, the formation process is accompanied by decreasing tilt angle of the sidewalls, guiding the ionization filamentation direction of the subsequent light field and sweeping across the sidewall region. It corresponds to the areas of "microcracks" and "induced stripes" on both sides of the microstructure. |
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来源
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中国激光
,2023,50(24):2402101 【核心库】
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DOI
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10.3788/CJL230834
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关键词
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激光技术
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飞秒激光微加工
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泵浦探测阴影成像
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多脉冲烧蚀
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等离子体
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地址
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1.
中国科学院西安光学精密机械研究所光子制造系统与应用研究中心, 陕西, 西安, 710119
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中国科学院大学, 北京, 100049
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语种
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中文 |
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文献类型
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研究性论文 |
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ISSN
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0258-7025 |
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学科
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电子技术、通信技术 |
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文献收藏号
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CSCD:7637435
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