Gold Surface Nanostructuring with Ultrashort Laser Pulses - Study of Non-equilibrium Effects

Laser material interaction and structure formation in metals under controlled ultrashort laser pulse conditions are discussed in this work. A novel approach is presented describing the exact amount of energy deposited by a laser pulse in a gold surface, applicable under a variety of structuring conditions. The presented model is validated by a new introduced broad-band pump-probe reflectivity measurement method. A technique also applicable to investigate other phenomenas where 20 fs resolution combined with an octave spanning spectral range is required. Here the observed dynamic energy absorption is probed by this method and is a factor not yet included in simulations dealing with surface structure formation, however can significantly influence the results. The amount of energy introduced in a surface determines the evolution of the material in the following few ps and ns, in which melting, ablation and finally crystallization in its final observable structure occurs. The influence of these dramatic laser induced phenomena is investigated in the second part of this work on the formation of periodic nanostructures. The experimental results obtained in this work are compared to a large-scale molecular dynamics simulation, conducted by D.S. Ivanov. The novelty of this approach is the scale which the model calculations and the experiment covers, combining the microscopic description of the electrons around the core with the macroscopic effects which an overheated melt has on the structure formation on the μm scale. The DFT calculations of the elevated electrons around the core were conducted by E.S. Zijlstra. The interpretation of the obtained results presented in this work leads to a deeper understanding of the involved process during the interaction of highly energetic ultrashort pulses with metals.