LAUSR

Abstract Laser ablation of mercury is investigated with the help of acoustical monitoring method which uses pulsed modulated laser intensity and piezo-transducer under the irradiated target. Two different trains consisting of 6 and ~70 short peaks (60 ps each) divided with 8 ns intervals are used. The method permits to detect effective displacement of the irradiated surface provided some necessary conditions are fulfilled. The paper purpose is to study influence of possible metal-nonmetal transition on the considered approach. It is found that the observed values of the effective displacement cannot be explained in the framework of a simple surface vaporization model. Another interpretation of the results which uses assumption about metal-nonmetal transition is proposed. The assumption is in accordance with our main results: observation of significant acoustic signal shift (70 ns) to earlier times and the signal widening at higher laser fluences (7 J/cm2) for the case of relatively smooth 30 ns laser pulse. Initial part (10 ns) of the shift is observed as well for the train consisting of 6 peaks. The obtained new experimental results can be considered as the first demonstration of metal-nonmetal transition during nanosecond laser ablation.