Structuring with excimer lasers—experimental and theoretical investigations on quality and efficiency

Manufacturing with excimer lasers is becoming an established technology in microstructuring, drilling, and laser vapor deposition. In this article an overview of the work will be given that was recently performed at the IFSW on excimer laser ablation concerning the quality and the efficiency of the ablation process. In a first part the setup used for the ablation experiments is presented. A beam homogenizer developed at IFSW is explained in more detail. The development of this device was initiated by the need for high beam quality along the whole propagation path. Results with modelings including three-dimensional heat conduction and multiple reflections of the incident beam at the hole walls will be compared with experimental findings. It will be shown that multiple reflections are responsible for the inhomogeneity of the bottom structure and can explain the quality of the ablated structure. Additionally, a few two- and three-dimensional structures obtained by using the presented setup and different working strategies will be introduced. The second part is concentrated on the efficiency of the ablation process. Investigations concerning material vapor expansion in the surrounding atmosphere, and the diagnostic studies of the interaction between this vapor and the incident laser beam during the pulse will be presented. The ablated material vapor/plasma strongly influences the process efficiency due to absorption of up to 80% of the incident laser energy. A model describing the vapor expansion and the interaction mechanisms between vapor, clusters condensed in the vapor, and the laser radiation can explain the decrease of the process efficiency due to absorption of the laser radiation by Mie scattering and inverse bremsstrahlung. The possible influence of the absorption and the material vapor expansion on the deposition of debris and a correlation of the diameter of the area covered with debris with the material vapor luminescence will be given.