M. Jupé
D. Ristau

Determination of material parameters for modelling of ultra-short pulse ablation threshold in transparent, dielectric material

11th International Conference on Photo-Excited Processes and Applications (ICPEPA 11)
13. September
Type: Konferenzbeitrag
With respect to material structuring, the ablation of dielectric materials is an important issue. To limit the damage zone during the material processing, the applied energy densities are close to the damage threshold. In theoretical descriptions of these processes, the excitation of the valence band electrons is calculated. Generally, a combination of photoionization (multiphoton and tunnel ionization) and avalanche ionization is used. Especially the Keldysh theory is based on the assumption that the material has a crystalline structure. Often, this theory is also used for amorphous solids. However, several parameters are not defined for amorphous dielectrics. For instance, amorphous materials do not have a well-defined band structure. Also, the model of the effective mass of the electrons is established on a periodic structure. Nevertheless, these parameters are utilized in calculations for amorphous structures. Especially the effective mass of the electrons is a pure fitting parameter. In this presentation, different theoretical and experimental approaches are discussed determining the respective parameters. For the theoretical calculation, the concept of the virtual coater has been established. This approach combines transport and atomistic thin film growth simulations as well as ab-initio methods which enable the electronic structure to be calculated. The virtual coater includes the specific growth conditions, which influence the atomistic structure, and consequently, the electronic and optical properties. Because of fundamental problems experienced when calculating the effective mass in non-periodical solids, an experimental approach is applied. Here, quantized nanolaminates are deposited and evaluated experimentally. Finally, the extracted parameters are used to calculate the ablation threshold of hafnia or tantala. The results are verified by experimental studies.