飞秒激光加工熔融石英的理论和实验研究  

Theoretical and experimental research of femtosecond laser processing fused silica

作　　者：潘鹏晖 吉鹏飞 林根 董希明 赵晋晖 Pan Peng-Hui;Ji Peng-Fei;Lin Gen;Dong Xi-Ming;Zhao Jin-Hui(Laser Micro/Nano-Fabrication Laboratory,School of Mechanical Engineering,Beijing Institute of Technology,Beijing 100081,China)

机构地区：[1]北京理工大学机械与车辆学院,激光微纳制造研究所,北京100081

出　　处：《物理学报》2022年第24期408-419,共12页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:51705234)资助的课题。

摘　　要：对单脉冲飞秒激光加工熔融石英进行了理论和实验研究,在追踪自由电子密度、温度和激光强度时空分布的基础上,量化了飞秒激光辐照熔融石英的电子动力学及瞬态材料光学和热物理的演变过程.通过将理论预测的烧蚀阈值、深度及轮廓,和实验结果进行比较,发现了理论预测结果与实验测量结果较好吻合,验证了本文所提出的理论模型的有效性.并进一步通过理论模型,揭示了在不同飞秒激光能量密度(也称“激光通量”)和脉冲持续时间(也称“脉冲宽度”)的辐照下,光致电离和碰撞电离中的自由电子弛豫时间演变规律,发现了自由电子弛豫时间对材料光学性质的演变和飞秒激光能量吸收过程起着至关重要的作用.理论模拟和实验测量均发现激光能量密度对烧蚀坑的形状有很大影响,即在激光能量密度略高于烧蚀阈值时烧蚀体积与激光能量密度呈线性关系.相较于皮秒激光而言,在飞秒激光辐照下烧蚀体积随着激光能量密度的增加而增大更为明显.因此,本文提出在略高于烧蚀阈值时可获得较高的加工效率,而在远高于烧蚀阈值时可获得良好的可重复性加工.The ablation threshold,depth and crater shape of fused silica for femtosecond laser processing are investigated theoretically and experimentally.Based on tracking the spatiotemporal distribution of the free electron density,free electron temperature,and laser intensity,the electron dynamics as well as the transient optical and thermophysical properties of femtosecond laser irradiated fused silica are quantitatively determined.The numerical model is validated by comparing the calculated threshold fluence,depth and crater shape of ablation with the experimentally measured ones at a wavelength of 800 nm.The free electron relaxation time at different laser fluences and pulse durations throughout the photoionization process and impact ionization process are probed.In the present work,the findings are as follows.1)The electron relaxation time significantly affects the material optical properties and femtosecond laser energy absorption.The optical properties change dramatically.The fused silica becomes opaque for the case of laser irradiation with fluence higher than the ablation threshold.Moreover,the transition from electron-phonon collision to electron-ion collision accompanies with the femtosecond laser ablation of fused silica.2)By using the proposed model,the experimentally observed saturation of ablation depth at high laser fluence is elucidated by the significant change of optical reflectivity and absorption coefficient.Both the results of theoretical simulation and experimental observation indicate that laser fluence has a strong influence on the shape of the ablation crater.The ablation volume increases sharply with the increase of laser fluence for femtosecond laser irradiation,compared with that for picosecond laser irradiation.3)With the increase of femtosecond laser fluence,the ablation depth removal efficiency and ablation efficiency are both saturated,followed by slight decrements.The peak of ablation depth removal efficiency peak occurs at the femtosecond laser fluence close to 1.4 times of the ablation

关 键 词：飞秒激光 激光与材料相互作用 介电材料 自由电子弛豫时间 

分 类 号：TN249[电子电信—物理电子学]