We investigated the dynamics of laser generated ablation plasma plume expanding in ambient air and dynamics of the sound wave generated by the expanding plasma. The ablation plasma plume was generated during nanosecond laser micromachining of the thin metal foil. The time-resolved images of the expanding plasma plume and sound wave were captured at several nanosecond intervals. Using captured images the expansion rate of the plasma plume was determined. The initial velocity of the plasma was found to vary from 6.0·10 3 m/s ± 0.3·10 3 m/s to 7.3·10 3 m/s ± 0.3·10 3 m/s depending on the laser fluence. The initial velocity of the sound wave generated by the expending plasma plume also varies with laser fluence. We also investigated sound wave using acoustic microphone. Based on obtained results we proposed a method for automatic focusing of the laser beam before laser micromachining that involves sound wave acoustic signal analysis.

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