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Femtosecond laser microprocessing of aluminum films and quartz
Laser micro and nano-machining using sub-picosecond laser pulses has become a very active area of research, driven by the development of more user-friendly lasers. An improved understanding of the advantages and limitations of using these lasers when processing various materials is desirable. ^ Ablation of 20 nm thick aluminum films was carried out using pulse widths from 300 fs to 6 ns to achieve sub-micron ablation diameters. Resolution and quality of the resulting craters is compared and discussed. The minimum crater diameter obtained with complete ablation of the film was 130-260 nm for a 400 nm wavelength, 400 fs pulse focused with a microscope objective with numerical aperture of 0.85. A large window of pulse energies exists where clean ablation of 20 nm Al films can be obtained with minimal damage to the substrate for pulses shorter than 4 ps. This pulse energy range was a factor of 2.6-7.3 times the ablation threshold for pulses less than 4 ps and decreased with increasing laser pulse width to ≤1.2 for 6 ns pulses. Nanoscale protusions (nanobumps and nanospikes) with heights from 20-140 nm were created at fluences just below the ablation threshold. The laser damage threshold of the film is also measured and compared to a theoretical model. ^ The quality of fs-laser micromachined quartz crystals was also examined. Fluence was varied and the entrance and exit side examined for microcracking to determine optimal processing parameters. Cuts with a high quality laser entrance side without microcracking could be obtained for fluence ranges from 2.5-13 J/cm2 while microcracking at the cut entrance is observed at 16 J/cm2. Damage on the exit side of the sample was observed within a distance of 50 μm from the center of the cut and runs parallel to the laser cut. ^
Engineering, Electronics and Electrical
Doerr, David W, "Femtosecond laser microprocessing of aluminum films and quartz" (2007). ETD collection for University of Nebraska - Lincoln. AAI3273191.