Experimental and Theoretical Investigation of Periodic Nanostructuring of Au with Ultrashort UV Laser Pulses near the Damage Threshold

The mechanism of surface restructuring by ultrashort laser pulses involves a number of fast, nonequilibrium, and interrelated processes while the solid is in a transient state. As a result, the analysis of the experimental data cannot address all of the mechanisms of nanostructuring. In this paper, we present a direct comparison of a simulation and the experimental results of surface nanomodifications induced by a single laser pulse. The experimental results are obtained by using a mask-projection setup with a laser wavelength of 248 nm and a pulse length of 1.6 ps. Two-beam interference of this short wavelength allows for producing a large-area intensity grating of 40 mu m in diameter on a gold surface with a sinusoidal shape and a period of 500 nm. The formed structures are analyzed at the surface and in a cross section by a scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Then a hybrid atomistic-continuum model capable of capturing the essential mechanisms responsible for the nanostructuring process is used to model the interaction of the laser pulse with a thick gold target. The good agreement between the modeling results and the experimental data justifies the proposed approach as a powerful tool revealing the physics behind the nanostructuring process at a gold surface and providing a microscopic insight into the dynamics of the structuring processes of metals in general. The presented model, therefore, is an important step towards a computational tool for predicting a materials response to an ultrashort laser pulse on the atomic scale. This detailed understanding of the dynamics of the process will pave the way towards predesigned topologies for functionalized surfaces on nanoscales and microscales.