Study of the dynamics of UV femtosecond laser ablation
It is well known that material processing with ultrashort laser pulses provides a significantly increased precision compared to that achieved by standard technologies. The reason for this improvement is the onset of rapid structural changes of the irradiated material preceding its ablative removal. As a result, the material surrounding the irradiated region will be negligibly affected by heat diffusion, thus facilitating the creation of high resolution patterns. A full understanding of the fundamental microscopic mechanisms underlying the generation of nanostructures on surfaces is however still missing. On the other hand, this knowledge should help us to fabricate tailored surface structures with sub-100 nm resolution. This capability would open up new possibilities for the creation of particular functionalities. Firstly, our objective is to study the dynamics of the formation of periodic nano-structures. For their creation ultrashort UV pulses are used to insure the highest possible spatial resolution. An appropriate choice of the irradiated volume allows considering a limited number of atoms, thus making it feasible to describe the whole process by molecular dynamic simulation (in collaboration with the University Kassel and the TU Kaiserslautern). This strategy makes it possible for the first time to compare theory and experiment on the same temporal and spatial scale.
In the experiments, the structures with periods in the range of 270-500 nm are produced by a mask projection setup. By selecting only the ± 1st diffraction orders in the Fourier plane, we can ensure that a sinusoidal intensity distribution will be created on the sample surface. The laser pulses are delivered by a frequency tripled Ti:Sa system seeding a KrF excimer amplifier running at a wavelength of 248 nm with a pulse length of 1.6 ps.
The results show a good agreement between the simulated cross section of the irradiated area and the experimentally measured topology of the structured sample, with void formation below the surface and an uplift of material in the area above.
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Laser-Laboratorium Göttingen e.V. (LLG)
Head of the Department
Dr. Peter Simon
"Short Pulses / Nanostructures"
Contact person for
Nano Structure Technology:
Dr. Jürgen Ihlemann