Cavitation dynamics of laser ablation of bulk and wire-shaped metals in water during nanoparticles production

Abstract

Although the first nanoseconds to microseconds rule the resulting process yield of laser ablation in liquid, a comprehensive view involving combination of time-resolved measurement techniques is still lacking. In this paper, fundamental aspects of laser ablation of metals in water during the production of nanoparticles are discussed. Three fast diagnostic methods have been applied simultaneously. These are Optical Emission Spectroscopy for the plasma characterization, fast shadowgraph for plasma and cavitation bubble dynamics and laser scattering for the mechanisms of delivery of the produced materials in the liquid. Moreover, in order to validate the discussion, the effect on cavitation dynamics of the ablation of bulk and wire-shaped targets has been investigated together with the relative nanoparticles production yield. Unusual arrow-bow ejection phenomena between the cavitation bubble and the wire result in suppressed material back-deposition, causing efficient ejection of ablated matter into the liquid. The presented nanosecond and microsecond-resolved analysis allows estimating the timescale and role of the basic mechanisms involved in laser ablation in liquids as well as the thermodynamic characteristics of the processes.

Cavitation bubble dynamics during pulsed laser ablation of a metallic glass in water

“…At that moment, the plasma expansion, which firstly experienced a fast-growing stage, also becomes stable. These calculated results are consistent with the observation that the plasma reaches the maximum volume after a few hundred nanoseconds [18,23]. Wu et al [19] have also found that, for the ∼1 GW/cm 2 laser ablation, the plasma length can only expand in 1 µs after the laser peak.…”

“…First, the stable state of the plasma induced by laser ablation can be regarded as the nucleation point of the cavitation bubble. This process is theoretically modeled in the present letter, although its experimental evidence is clear [18,23]. Second, the initial evolution of the first bubble is accompanied by the target's ablation in the form of an explosive boiling [14].…”

“…It usually requires the nucleation state of a bubble as additional adjusting parameters [8] or resorts to the experimental measurements [7,22]. Actually, the bubble nucleation originates from the fast evolution of laser-induced plasma, which has been confirmed experimentally [18,23]. When the laser pulse with a near-Gaussian intensity profile I (t) is focused on the Vitreloy 1 target through water, atomization and ionization of the irradiated spot occur and a plasma is thus produced.…”

“…The first image captures the optically active plasma plume that has already expanded into the entire viewing window. Since the plasma lifetime is much shorter than the time between two frames [17][18][19], the first snapshot is regarded as a reference for time recording (t = 0 µs). The bubble expands for a duration of about 800 µs and then shrinks, followed by the collapse after 1440 µs.…”

Comparison of silver nanoparticles confined in nanoporous silica prepared by chemical synthesis and by ultra-short pulsed laser ablation in liquid

“…colloidal solutions have been obtained in water and organic solvents instantaneously [12][13][14]. Laser ablation in liquid is a low cost technique because it does not need vacuum equipment, not wet chemistry processes are required and the formed nanoparticles, being stored in the liquid as a colloidal dispersion, are easily collected after the synthesis.…”