Investigation of laser-induced structures on metal surfaces produced via two-beam and laser-plasmon interference
von Jens Oltmanns
Datum der mündl. Prüfung:2022-12-09
Betreuer:Dr. Peter Simon
Gutachter:Prof. Dr. Alexander Egner
Gutachter:Prof. Dr. Hans Christian Hofsäss
EnglischPeriodic surface structures can change the properties of material surfaces. The obtained various functionalities strongly depend on the type of the specific structures. This work deals with the generation of periodic structures on metal surfaces using ultrashort pulse lasers. Both, deterministic structures by superposition of mutually interfering beams, as well as ripple structures (laser-induced periodic surface structures, LIPSS) by a single beam irradiation, are generated and the resulting structures are evaluated. The parameters such as the wavelength of the laser, the pulse duration, the fluence distribution and the surrounding medium are changes in the experiments and the changes in the structures analysed. In addition, the experimental findings are compared to simulation results to understand the fundamental processes of the structure formation. Structures were obtained using single pulse interference patterning on gold under solid and liquid confinement layers with different thicknesses. Femtosecond and picosecond laser pulses are used. The structures forming under the confinement layer have a smaller height and less debris. The height distribution under the liquid confinement layer are inhomogeneous when using the femtosecond pulse, attributed to a pressure bubble in the confinement layer, which is pushing the developing structures down- and sidewards. But with the picosecond pulse and under the solid layer the structures are homogeneous. LIPSS were produced on a gold surface using femtosecond pulses at different wavelengths (UV, green, IR), also with and without a confinement layer. The measured properties of the structures are in accordance with those predicted by the plasmonic theory, thus providing further evidence that LIPSS emerge as a result of interference between SPP and the incoming light. Furthermore, a method of controlling the structure heights is presented.
Keywords: LIPSS; laser-induced periodic surface structures; surface structuring; plasmon; laser; two-beam interference; confinement layer