Computational Investigation of Short Laser Pulse Nanostructuring of Dielectric Materials.

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Since recently ultrashort laser pulse irradiation has become a beneficial tool in achieving controlled laser-induced matter transformations and found a variety of applications in laser processing technologies such as generating three-dimensional structures, creation of color centers, and development of micro optics. With the help of femtosecond laser techniques, waveguiding objects were created in fused silica, which is one of the commonly used optical materials in both IT- and Bio-technologies.The interaction of ultrashort laser pulses with dielectrics, however, involves a number of competing non-equilibrium processes that can be activated in a wide range of temporal and spatial scales. The transient character of laser-induced phase transitions, occurring under conditions of strong superheating on a pico- and sub pico-second time scales and in the presence of strong pressure and temperature gradients, can result in ultrafast melting, spallation, ablation, and breakdown processes. Understanding of all these processes on an atomic scale and being able to precisely simulate them for predicting material behavior and hence designing new nano-technology applications requires a robust fundamental theory. In this project we propose to develop a combined computational method suitable for the investigation of the interaction of ultrashort laser pulses with dielectric solids. The effect of photo-excited free carrier dynamics will be described in the framework of a continuum approach, whereas the kinetics of laser-induced non-equilibrium phase transformation processes will be addressed at atomic level with the Molecular Dynamics (MD) method. For this purpose, the project assumes a close collaboration between the groups of Prof. Rethfeld (TU-Kaiserslautern) and the group of Prof. Garcia (University of Kassel). The laser-induced processes, constituting free carrier dynamics, will be thoroughly studied and described in the form of numerical blocks (for incorporation into MD code) in the group of Prof. Rethfeld. The corresponding MD interatomic potential, on the other hand, will be modified in the group of Prof. Garcia to account for interatomic bond weakening and description of the laser-induced non-thermal effects. The developed model will be applied to study the mechanism of ultrashort pulse laser-induced damage of dielectrics on the example with fused silica and crystalline beta-SiO2, which is of enormous technological relevance. Realized in large scale MD simulations, our proposed approach is expected to capture the above mentioned mechanisms and have a strong impact on both the fundamental understanding of the nanostructuring processes induced in dielectric solids and their possible technological applications.