Surface nanoprocessing with unfocused beams of high-energy femtosecond lasers: A tool to produce surface characteristics libraries

Abstract

We demonstrate a single-shot method for probing ultrafast laser–matter interactions using unfocused multi-terawatt femtosecond beams. The intrinsic fluence inhomogeneity of the beams is exploited to accomplish parallel, spatially encoded experiments performed under strictly identical conditions across a wide energy range in a single step, enabling systematic mapping of energy-dependent surface responses without beam scanning. As proof of the technique, the large set of simultaneously collected data points below, at, and above the threshold inherently allows for a threshold evaluation approach, different from both the diameter/depth regression analysis and the statistical method. Using copper as a test system, we quantify the fluence dependence of reflectance and morphology and identify a multi-pulse optical threshold of 0.020 J/cm2, coinciding with the onset of ablation confirmed by SEM imaging. The minimum specular reflectance observed, around 0.10%, favorably compares to the respective figures reported. Applying this parallelized surface mapping technique with high-energy laser systems featuring suitably large beam diameters thereby provides a versatile platform for exploring ultrafast laser-induced surface responses, with potential applications in material design, surface engineering, and optical damage studies.