Pump-probe microscopy of femtosecond laser ablation in air and liquids

The ablation process of femtosecond laser pulses of iron in air and different liquids was investigated for fluences of 0.5 J/cm(2) and 2 J/cm(2) by means of femtosecond pump-probe microscopy. Measurements of the relative change in reflectivity suggest that the surrounding liquid has a significant impact on the ablation process. During the heating phase of the metal within the first picoseconds after laser beam impact, the change in reflectivity in air and liquids is similar. Afterwards, the vapor and melt expulsion in air leads to a strong decrease in reflectivity, while the change in reflectivity in the liquids shows a more complex fluence and time-dependent behavior. This behavior is suggested to be triggered by the expansion of the molten surface and chemical reactions on the picosecond timescale.