Study of Femto/nano-second Laser Micro/nano-scale Machining
Shih-Hui Gilbert Chang
College of Engineering
Department of Engineering Science
|英文關鍵詞：||laser machining、femtosecond laser、sensor|
本論文著重脈衝雷射加工技術於提高加工精度、提高加工速率、以及感測器的製作等三方面，包含飛秒雷射加工以及奈秒雷射加工。藉由共軛焦(confocal)原理基礎所發展的深度量測系統用於雷射加工應用可彌補一般雷射加工所遇到加工深度未知的問題。由於雷射加工深度會受多變數的影響例如能量密度(fluence)、脈衝寬度、雷射波長等等，若能及時監控加工深度，對於加工精度可有顯著提升。此系統已成功整合於奈秒雷射加工機台之中，且其理想解析度可達0.5微米。更進一步，利用奈秒雷射的瞬間熱量傳遞效應，製造表面分布有高密度解均勻分布的金奈米粒子(nanoparticle)的雷射奈米結構化的試片並應用於表面增強拉曼散射(surface-enhanced Raman scattering，SERS)，其增強因子(enhancement factor)於量測分子為Rhodamine 6G且激發光波長為632.8 nm的條件下可達105。
Laser micromachining has been widely applied not only for industry but also for research demands. Nanosecond pulse laser systems are popular used in industry due to the high production throughput and low operation cost. However, the significant drawback of the laser systems is difficult to machine dielectric materials due to low absorptivity in wavelength range from visible to near infrared. Currently, the drawback has been addressed by femtosecond pulse lasers via multiphoton absorption induced by extremely high peak power. The femtosecond laser systems have opened a new window in laser micromachining.
In this thesis, pulse laser micromachining technologies including nanosecond laser micromachining as well as femtosecond laser micromachining were investigated and focused on improving the machining accuracy and throughput and developing sensors. A depth measuring technique for laser hole drilling was developed via the confocal principle to overcome the issue of the unknown machining depth during the laser machining because the machining depth is multiparameter-dependent factors such as laser fluence, pulse duration, wavelength, etc. The developed depth measuring system was successfully integrated into a nanosecond micromachining system with a resolution of 0.5 μm. Furthermore, employing the rapid thermal delivering characteristic of nanosecond laser pulses, a laser-nanostructured substrate with dense and high uniformity gold nanoparticles on the surface was fabricated by the nanosecond laser annealing of a gold thin film coated on silicon wafer. The laser machining substrate is utilized for surface-enhanced Raman scattering (SERS). An enhancement factor of 105 by comparing the normal Raman and SERS signals was demonstrated for the Rhodamine 6G sample at 632.8 nm wavelength excitation.
In the femtosecond machining, the machining with focus shaping was utilized to fabricate 3D microlens arrays including cylindrical lens and spherical lens at horizontal and vertical arrangements in photosensitive glass. Focusing quality and imaging testing were conducted to examine the performances of the fabricated microlens arrays. In the same photosensitive glass material, an optical fiber assisted Fabry-Perot interferometer embedded in a glass chip as a refractive index sensor for liquid samples was also developed. By machining silicon wafer substrates in silver nitrate solution with the femtosecond lasers, high sensitivity SERS substrates were produced and the enhancement factor was calculated as 109. Finally, a femto/nano-second dual-beam micromachining system has been developed and benefits the ablation efficiency on dielectric materials which are usually difficult to machine by other types of lasers such as continuous-wave laser and single nanosecond pulse laser.
Table Captions X
Figure Captions XI
Chapter 1 Introduction 1
1.1 Brief 1
1.2 Motivations 2
1.3 Outlines 3
Chapter 2 Mechanisms of Laser Micromachining 5
2.1 Nanosecond laser regime 5
2.2 Femtosecond laser regime 9
Chapter 3 Nanosecond Laser Machining 15
3.1 Nanosecond laser micromachining system 15
3.2 Depth measurement for micro-holes drilled by lasers 17
3.2.1 System setup 19
3.2.2 Experiments and results 26
3.3 Laser-treated substrate with nanoparticles for surface-enhanced Raman scattering 32
3.3.1 Fabrication 33
3.3.2 Results 34
3.4 A method to fabricate 2D nanoparticle arrays 41
3.4.1 Experimental results 43
3.4.2 Results and discussion 44
Chapter 4 Femtosecond Laser Machining 57
4.1 Femtosecond laser micromachining system 57
4.2 Fabrication of microlens array in photosensitive glass by femtosecond laser direct writing 58
4.2.1 Foturan glass material 60
4.2.2 Processing of Foturan glass 61
4.2.3 Microlens array fabrication 61
4.2.4 Results and discussion 66
126.96.36.199 Cylindrical microlens arrays 66
188.8.131.52 Spherical microlens arrays 70
184.108.40.206 Imaging testing 72
220.127.116.11 Potential applications 73
4.3 Fabry-Perot interferometer embedded in a glass chip fabricated by femtosecond laser 75
4.3.1 Theory 75
4.3.2 Design and fabrication 79
4.3.3 Results 80
4.4 One-step fabrication of nanostructures by femto- second laser for surface-enhanced Raman scattering 87
4.4.1 Experimental procedures 89
18.104.22.168 Sample preparation 89
22.214.171.124 SERS measurement 89
4.4.2 Results and discussion 90
126.96.36.199 Evaluation of nanostructures 90
188.8.131.52 Parametric study 95
184.108.40.206 Estimation of enhancement factor 97
Chapter 5 Dual-beam Laser Micromachining 101
5.1 System setup and experimental procedures 102
5.2 Experimental results 105
Chapter 6 Conclusions 109
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