Modeling of nanosecond pulsed laser processing of polymers in air and water

Abstract

Laser ablation of polymers in water is known to generate distinct surface characteristics as compared to that in air. In order to understand the role of ambient media during laser ablation of polymers, this paper aims to develop a physics-based model of the process considering the effect of ambient media. Therefore, in the present work, models are developed for laser ablation of polymers in air and water considering all the relevant physical phenomena such as laser–polymer interaction, plasma generation, plasma expansion and plasma shielding. The current work focuses on near-infrared laser radiation (λ = 1064 nm) of nanosecond pulse duration. The laser–polymer interaction at such wavelengths is purely photo-thermal in nature and the laser–plasma interaction is assumed to occur mainly by inverse-bremsstrahlung photon absorption. The computational model is based on the finite volume method using the Crank−Nicholson scheme. The model predicts that underwater laser ablation results in subsurface heating effect in the polymer and confinement of the laser generated plasma, which makes it different from laser ablation in air. Plasma expansion velocities are much lower in water than in air. This results in an enhanced plasma shielding effect in the case of water. The predicted results of ablation depth versus fluence from the model are in qualitative agreement with those observed in experiments.

Underwater Laser Treatment of PET: Effect of Processing Parameters on Surface Morphology and Chemistry

“…This may originate from the confined plasma plume in water, which expands at a much lower velocity than in air (order of magnitude less). This implicates that spatially confined plasma induces increase of surface temperature in water environment much intensively than in air [10], which may significantly contributes to the development of similar surface structure as in air when processing at sufficiently lower laser fluencies in water [15]. It is also obvious from the Figures 4-6, that the higher the laser fluence applied the more uniform developed nanostructure is and the possibility of modulation of fine microstructure by variation of applied voltage diminishes.…”

“…Although the fundamentals of the laser-matter interaction remain the same as in air even in the presence of water, such environment can have a significant effect especially to the heating of the polymer and in turn may result to the development of surface structures, which morphology is far away from those, typically observed in case of laser processed materials in air environment (LIPSS) [8,9]. In particular, the phenomena of plasma formation, its expansion, and subsequent radiation attenuation effects, are greatly influenced by the specific type of confining media [10].…”

Laser Direct Activation of Polyimide for Selective Electroless Plating of Flexible Conductive Patterns

“…The possible mechanism of the selective metallization of PI was further studied. The LISA process is usually implemented on other polymers in a water medium, − ,− which indicates that the laser process at the interface between water and PI is significant for an effective modified surface. By comparing the surface morphology of PI after laser irradiation in water and in air, the mechanism of laser modification at the interface could be speculated.…”

Numerical modeling to predict threshold fluence for material ejection in Laser-Induced forward transfer of metals

“…The pulsed laser beam generates thermal gradients in the donor film due to laser absorption and material heating governed by Fourier's law of heat conduction (equation ( 4)) [29]:…”

“…The carrier heats up only due to the heat conducted from the donor film. Hence, the governing equation for heating of the carrier is given by [29]:…”