Incubation Effect of Pre‐Irradiation on Bubble Formation and Ablation in Laser Ablation in Liquids

Abstract

Pulsed laser ablation in liquids (PLAL) is a multi‐scale process, which is widely studied either in batch ablation with prolonged target irradiation as well as mechanistic investigations, in a defined (single‐shot) process. However, fundamental studies on defined pulse series are rare. We have investigated the effect of a developing rough morphology of the target surface on the PLAL process with nanosecond pulses and, partially, picosecond pulses. At low fluence the cavitation bubble growth as well as the ablation yield depend on the irradiation history of the target. The bubble size increases with repeated irradiation on one spot for the first 2–30 pulses as well as with the applied dose. This is discussed within the framework of incubation effects. Incubation is found to be important, resulting in a bubble volume increase by a factor of six or more between pristine and corrugated targets. The target surface, changing from smooth to corrugated, induces a more efficient localization of laser energy at the solid‐liquid interface. This is accompanied by a suppressed reflectivity and more efficient coupling of energy into the laser‐induced plasma. Thus, the cavitation bubble size increases as well as ablation being enhanced. At high fluence, such incubation is masked by the rapid development of surface damage within the first shots, which eventually would lead to a reduction of bubble sizes.

Multi-pulse laser-induced bubble formation and nanoparticle aggregation using MoS2 nanoparticles

“…4. Factors such as the increase in pressure caused by the formation of the cavitation bubble 40,41 , changes in the optical force gradient 22 , and the surrounding medium can affect the bubble formation 42 . Differences in individual laser powers as well as the spatial and temporal overlap of the two pulses can change the profile of the force gradient of the optical trap and affect the heating of the bubble.…”

In situ speciation and spatial mapping of Zn products during pulsed laser ablation in liquids (PLAL) by combined synchrotron methods

“…By integrating the mass density over the whole bubble area we derive a mass of 2.2 × 10 −7 g, corresponding to a volume of ablated zinc of ≤1 μm depth at a presumed crater area of 0.04 mm 2 . The derived ablation depth is much larger than the laser absorption length in zinc and probably caused by 2 effects: corrugation of the surface during the ablation with several pulses per unit area 49 and a heat-affected zone that is considerable larger than the absorption length due to fast heat conduction by phonons and fast electrons. 68 While the total mass can be deduced from the absorption step height, the spectrum close to the edge can yield information about the ablated species.…”

“…The zinc wire (supported by the back wall) 48 is pulled through the chamber at a speed that replaces the irradiated spot within around 5 laser pulses in order to optimize the ablation efficiency. 49…”

“…Another observation is that the bubble surface is less smooth than observed earlier for PLAL on noble metals in the expanded phase. This might be due to the relatively strong ablation due to the low energy needed for evaporation of zinc as compared to other metals 49 as well as ablation of pre-deposited nanoparticles in a multishot exposure. Part of the ablated mass may have sizes large enough to penetrate the bubble interface to cause ripples.…”

“…20,25 Due to the strong averaging over a sequence of pulses the spatial distribution may be blurred, given that individual bubble sizes can vary with corrugation of the substrate. 49,61 Fig. 1 Visible stroboscopic images (left column), X-ray multicontrast images (center column, pink: dark-field contrast, gray: absorption contrast) and Zn K-edge X-ray absorption spectra (right column) as function of delay in microseconds after laser irradiation.…”