| Summary: | 博士 === 國立成功大學 === 工程科學系碩博士班 === 98 === 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.
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