## 5 Conclusions  
Modeling of pulsed laser radiation on an Al alloy target was performed, using a single pulse of 6-ns duration and energy of 0.7 mJ that induced changes, in a predefined surface roughness pattern, in the plastic and melting regimes. The induced changes were also experimentally visualized by a white light profilometry setup with submicrometer resolution. FEM thermal-structural analysis was carried out to model the laser-irradiated rough surface, performing downscale modeling for surface roughness level of the experimentally obtained surface roughness profile. Each one of the sequentially developed multiscale models can simulate the thermal-mechanical laser-solid interactions, according to the irradiated area of interest and the surface roughness profile therein, with a predefined geometrical accuracy. The numerical and experimental results presented a qualitative and quantitative agreement and determined the scale (micro- and/or nanoscale) and the nature of the changes that took place. The correlation of the experimental measurements to the simulation findings was obtained by the comparison of the experimentally measured and numerically computed fractured volume of the workpiece. In our future work, we aim to extend the capabilities of the FEM model on the modification and control of the morphological behavior of the surface roughness profile under a sequential irradiation of laser pulses. The corresponding experiments that will be performed and compared to the numerical outcomes will provide a complete surface roughness modification and control method.  
The determination of these positions, where changes in surface roughness take place after their interaction with a single laser pulse in this energy regime, is of major importance. Applications where changes of matter of micro- or nanoscale order affect the material structure depend on this knowledge, since at these scales different types of cracks may initialize, ripples may be formed, and mechanical and optical materials' properties may change. Furthermore, the combination of numerical modeling with the experimental methodology presented in this study constitutes a promising tool for an in-depth analysis of the influence of heat parameters on the surface roughness of solid materials and can be further extended to various laser-solid interactions, such as laser machining and micro-machining applications, solid materials' testing using generated ultrasounds, and laser material processing. Higher spatial modeling of the micro-roughness characteristics will be further included in future work that will concern the influence of the surface roughness on the generation and propagation of ultrasounds based on the knowledge gained from this work, while the energy absorption on the rough surface will be treated by initially performing a ray-tracing analysis.  
E.K. performed the simulations. Experiments were carried out and analyzed by [PERSON], K.K., A.S., and I.F. [PERSON], [PERSON], and M.T. supervised the laser-target interaction experiments. [PERSON] contributed to the results' analysis. [PERSON] proposed the main idea, supervised the studies, and was responsible for the writing of this article along with E.K. and K.K. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the following funding schemes: (1) \"ELI--LASERLAB Europe Synergy, HiPER& IPERION-CH.gr\" (MIS 5002735) which is implemented under the Action \"Reinforcement of the Research and Innovation Infrastructure\", funded by the Operational Programme \"Competitiveness, Entrepreneurship and Innovation\" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund), (2) This research/work was partially carried out within the framework of the IAEA Coordinated Research Project F13020 \"Pathways to Energy from Inertial Fusion--Materials Research and Technology Development\".