The ablation process of materials by an excimer laser is in most cases of thermal nature. The high intensity of the laser radiation leads within a few nanoseconds to evaporation of the material which compresses the ambient gas. A strong shock wave and further discontinuities are formed. These gasdynamic processes were detected by schlieren photography and shadowgraphy. The investigations show that the propagation mechanism of the shock wave depends on the ambient gas pressure and the laser pulse energy. The measured distances are compared with the calculated values using the Sedov-Taylor blast wave theory. A very good agreement between theoretical values and experimental data is found. Further, an interpretation of the appearance of the other discontinuities and their behavior will be given. A special nozzle was constructed in order to form a 1D gas flow. The modeling of this gas flow leads to the density, pressure and velocity of the jet at any point of the gas flow. The presence of such an external gas jet parallel to the target surface shows a drastical effect on the gasdynamic processes as well as on the formation of debris.
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