Toward the optimization of double-pulse LIBS underwater: effects of experimental parameters on the reproducibility and dynamics of laser-induced cavitation bubble

Abstract

Double-pulse laser-induced breakdown spectroscopy (LIBS) was recently proposed for the analysis of underwater samples, since it overcomes the drawbacks of rapid plasma quenching and of large continuum emission, typical of single-pulse ablation. Despite the attractiveness of the method, this approach suffers nevertheless from a poor spectroscopic reproducibility, which is partially due to the scarce reproducibility of the cavitation bubble induced by the first laser pulse, since pressure and dimensions of the bubble strongly affect plasma emission. In this work, we investigated the reproducibility and the dynamics of the cavitation bubble induced on a solid target in water, and how they depend on pulse duration, energy, and wavelength, as well as on target composition. Results are discussed in terms of the effects on the laser ablation process produced by the crater formation and by the interaction of the laser pulse with floating particles and gas bubbles. This work, preliminary to the optimization of the spectroscopic signal, provides an insight of the phenomena occurring during laser ablation in water, together with useful information for the choice of the laser source to be used in the apparatus.

LIBS Analysis of Liquids and of Materials Inside Liquids

“…It has been hypothesized that these hot particles, analogue to a black-body radiators, also contribute to an intense continuum emission [89]. The particles expulsed by ablation or those formed later by clustering [91,92] are responsible for the radiation loss of the successive pulses through scattering, and might induce also the plasma formation away from the target. For these reasons, in laboratory conditions the liquid should be frequently exchanged or the fresh liquid should be flushed through the cell.…”

“…8.17. In both cases the particles generated by previous laser shots disturb the formation of the plasma and the successive bubble growth [92]. Instabilities in the bubble formation and growth further contribute to fluctuations of DP LIBS signal, and here the data filtering becomes important [70].…”

Comparison of the overall temporal behavior of the bubbles produced by short- and long-pulse nanosecond laser ablations in water using a laser-beam-transmission probe

“…The laser-induced bubble repeats expansion and contraction in the scale of a few hundred microseconds, which can be well described by the Rayleigh-Plesset equation [5][6][7][8][9], while the plasma disappears in a few microseconds. The bubble dynamics is quite interesting for fundamental research, while it plays an important role for the underwater elemental analysis [10][11][12][13][14][15][16][17] and the synthesis of nanoparticles [18][19][20][21][22][23][24][25].…”

“…The effects of the laser parameters on the laser-induced bubble in bulk water (Vogel et al [26,27]) and on the bubble produced by the laser ablation in water (Cristoforetti et al [10]) have been studied. The behavior of the laser-induced bubble has been mainly studied in the pulse duration ranging from femtoseconds to short-nanoseconds so far [10,26,27].…”

“…The behavior of the laser-induced bubble has been mainly studied in the pulse duration ranging from femtoseconds to short-nanoseconds so far [10,26,27]. On the other hand, it has been clarified that the relationship between the plasma and the bubble is very important to obtain intense and narrow optical emission spectral lines for the underwater elemental analysis, and the relationship can be controlled by changing the pulse duration in the range from ten to hundred nanoseconds [16,17].…”