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Laser-induced cavitation bubble has been widely used to investigate the mechanisms of hydraulic machinery cavitation erosion and to explore applications in atomization, alloy strengthening, ultrasonic chemistry, biomedicine, surface cleaning and materials processing. This paper consolidates existing research findings on the cavitation bubble dynamics near different boundaries and provides insights for future research work. Firstly, the dynamics of a single cavitation bubble in an infinite field is presented. Subsequently, the focus shifts to the dynamics of cavitation bubble near a rigid wall, angular walls, particles and hydrofoil. Lastly, the paper delves into the dynamics of cavitation bubble within a droplet, revealing the microscopic mechanism of droplet breakup induced by cavitation bubble.

Repeated single cavitation bubble experiments were performed primarily on 316L stainless steel, and some on nickel–aluminum–bronze (NAB) and pure aluminum. The bubble dynamics were recorded with two high-speed cameras and correlated with surface images, also acquired in situ. These experiments were performed for a range of stand-off distances γ (the ratio of the distance of the solid surface from the bubble to the bubble’s maximum radius) from 0.3 to 2.15. For all stand-off distances, single pits were the only surface change detected at the beginning of damage formation. Later phases of the collapse are not axisymmetric but show regions of “stronger” collapse, and the pits occur on the material underneath those regions. For γ  < 0.4, the damage is attributed to the second collapse. For γ  > 0.4, the first bubble collapse is most likely responsible for pitting. Shock-wave emission was detected from the collapse regions that were linked to the damage. On 316L, the pitting rate was found to be linearly dependent on the bubble radius, indicating a non-zero lower limit for the bubble radius below which pits do not occur. In terms of stand-off distance, the pitting rate (defined here as average pits per bubble) was non-monotonic, with maxima for bubbles initiated closest to the sample ( γ  = 0.3) and at γ  = 1.4.

The dynamics of a laser-induced bubble on top of a solid cylinder is studied both experimentally and numerically. When the bubble is generated close to the flat top along the axis of the cylinder and its maximum radius exceeds the one of the flat top surface, it collapses in the form of a mushroom with a footing on the cylinder, a long stem and a hat-like cap typical for a mushroom head. The head may collapse forming a thin, fast liquid jet into the stem, depending on bubble size and bubble distance to the top of the cylinder. Several experimental and numerical examples are given. The results represent a contribution to understand the behavior of bubbles collapsing close to structured surfaces and in particular, how thin, fast jets are generated.

We report a new regime of filamentation in water in tight focusing geometry, very similar to the so-called superfilamentation seen in air. In this regime there is no observable conical emission and multiple small-scale filaments, but instead a single continuous plasma channel is formed. To achieve this specific regime the principal requirement is the usage of tight focusing and supercritical power of laser radiation. Together they guarantee extremely high intensity in the microvolume in water (∼1014 W cm−2) and clamp the energy in the ultra-thin (approximately several microns) channel with a uniform plasma density distribution in it. Each point of the 'superfilament' becomes a center of spherical shock wave generation. The overlapped shock waves transform into one cylindrical shock wave. At low energies, a single spherical shock wave is generated from the laser beam waist, and its radius tends toward saturation as energy increases. At higher energies, a long stable contrast cylindrical shock wave is generated, whose length increases logarithmically with laser pulse energy. The linear absorption decreases the incoming energy delivered to the focal spot, which dramatically complicates the filament formation, especially in the case of loose focusing. Aberrations added to the optical scheme lead to multiple dotted plasma sources for shock wave formation, spaced along the axis of pulse propagation. Increasing the laser energy launches the filaments at each of the dots, whose overlapping leads to enhancing the length of the whole filament and therefore the shock impact on the material.

To investigate the plasma shielding of laser-induced cavitation bubbles near a wall, a pulsed laser with different energies was selected to induce cavitation bubbles on the surface of 7050-T7451 aluminum alloy. A high-speed camera captured the evolution of the cavitation bubble, while a fiber-optic hydrophone system collected the acoustic signals during the evolution. Finally, a confocal microscope was used to view and analyze the surface morphology of 7050 aluminum alloy. The experimental results indicate that as the laser energy increases, the diameter, the evolution time, the pressure of the bubble, and both the pit diameter and depth all increase. Beyond an energy level of 1.4 J, the maximum diameter and the evolution time of the laser-induced cavitation bubble begin to decrease; the maximum diameter decreases by 2.04%, and the first evolution time decreases by 3.26%. Plasma shielding was observed in this experiment. Considering that the essence of a laser-induced cavitation bubble is the interaction between a high-energy laser and a liquid medium, the abnormal decrease in the maximum diameter, evolution time, and sound pressure epitomizes the manifestation of plasma shielding.

To investigate the feasibility and formation laws of fabricating micro-dimples induced by near-wall laser-induced cavitation bubble (LICB) on 7050 aluminum alloy. A high-speed camera and a fiber-optic hydrophone system were used to capture pulsation evolution images and acoustic signals of LICB. Meanwhile, a three-dimensional profilometer was employed to examine the contour morphology of the surface micro-dimple on the specimen. The results show that at an energy level of 500 mJ, the total pulsation period for the empty bubble is 795 μs, with individual pulsation periods of 412.5 μs, 217 μs, and 165 μs for the first, second, and third cycles, respectively, with most energy of the laser and bubble being consumed during the first evolution period. Under the synergy of the plasma shock wave and collapse shock wave, a spherical dimple with a diameter of 450 μm is formed on the sample surface with copper foil as the absorption layer. A model of micro-dimple formed by LICB impact is established. As the energy increases, the depth of the surface micro-dimple peaks at an energy of 400 mJ and then decreases. The depth of the surface micro-dimple increases with the increase in the number of impacts; the optimal technology parameters for the micro-dimple formation by LICB impact are as follows: the absorption layer is copper foil, the energy is 400 mJ, and the number of impacts is three.

Laser-induced acoustic cavitation microbubble dynamics have exhibited significant development in biological systems such as lithotripsy. Investigating the mechanically laser-induced acoustic cavitation microbubble in viscoelastic tissue is the goal of this work. Based on surface tension and viscous forces, the laser-induced cavitation model (also known as the modified Rayleigh–Plesset model), the theoretical model is developed and numerically solved using exponential cubic B-spline Collocation Method. In addition, the energy released in viscoelastic tissue by laser-induced acoustic cavitation as well as mechanically induced cavitation is investigated. The findings of our work provide valuable insight into the application of laser-induced acoustic cavitation microbubbles such as kidney stones and lithotripsy.

A bubble expanding and collapsing near a solid boundary develops a liquid jet toward the boundary. The jet leaves a torus bubble and induces vortices in the liquid that persist long after the bubble oscillations have ceased. The vortices are studied numerically in axial symmetry and compared to experiments in the literature. The flow field is visualized with different methods: vorticity with superimposed flow-direction arrows for maps at a time instant and colored-liquid-layer flow-field maps (dye advection) for following the complete long-term fluid flow up to a chosen time since bubble generation. Bubbles with equal energy—maximum radius in a free liquid Rmax∞= 500 µm—are studied for different distances Dinit from the solid boundary. The interval of normalized distances D* = Dinit/Rmax∞ from 0.4 to 1.8 is covered. Two types of vortices were reported in experiments, one moving toward the solid boundary and one moving away from it. This finding is reproduced numerically with higher resolution of the flow field and in more detail. The higher detail reveals that the two types of vortices have different rotation directions and coexist with individually varying vorticity amplitude throughout the interval studied. In a quite narrow part of the interval, the two types change their strength and extent with the result of a reversal of the dominating rotational direction of the fluid flow. Thereby, the experimentally found transition interval could be reproduced and refined. It is interesting to note that in the vortex transition interval, the erosion of a solid surface is strongly augmented.

Cell oxygenation and nutrition are crucial for the viability of tissue-engineered constructs, and different alternatives are currently being developed to achieve an adequate vascularisation of the engineered tissue. One of the alternatives is the generation of channel-like patterns in a bioconstruct. Here, the formation of full-formed channels inside hydrogels by laser-induced cavitation was investigated. A near-infrared, femtosecond laser beam focused with a high numerical aperture was employed to obtain intra-volume modifications of a block of gelatine hydrogel. Characterisation of the laser-processed gelatine was carried out by optical microscopy and epifluorescence microscopy right after and 24 h after the laser process. Rheology analyses on the unprocessed gelatine blocks were conducted to better understand the cavitation mechanism taking place during the intense laser interaction. Different cavitation patterns were observed at varying dose values by changing the repetition rate and the overlap between successive pulses while keeping the laser fluence and the number of passes fixed. This way, cavitation bubble features and behaviour can be controlled to optimise the formation of intra-volume channels in the gelatine volume. Results showed that the generation of fully formed channels was linked to the formation of large non-spherical cavitation bubbles during the laser interaction at high dose and low repetition rates. In conclusion, the formation of fully formed channels was made possible with a near-infrared, femtosecond laser beam strongly focused inside gelatine hydrogel blocks through laser-induced cavitation at high dose and low repetition rates.

The disinfection and removal of biofilm from titanium dental implants remains a great challenge in oral medicine. Here we present results of novel photoacoustic irrigation laser modalities for biofilm removal in model geometries mimicking the peri-implant pocket. The efficacy of single pulse (Er:YAG-SSP) and dual pulse (Er:YAG-AutoSWEEPS) photoacoustic irrigation modalities were determined for Enterococcus faecalis biofilm decontamination from titanium surfaces in narrow cylindrical and square gap geometries. The density of bacteria as well as the number of live bacteria were determined prior and after different photoacoustic treatments. Both SSP and AutoSWEEPS photoacoustic irrigation techniques removed at least 92% of biofilm bacteria during the 10 s photoacoustic treatment. The effectiveness of cleaning was better in the narrow square gap geometry compared to the cylindrical geometry. The dual pulse Er:YAG-AutoSWEEPS photoacoustic irrigation showed better results compared to SSP modality. No chemical adjuvants were needed to boost the effectiveness of the photoacoustic irrigation in the saline solution. The results imply that photoacoustic irrigation is an efficient cleaning method for debridement and decontamination in narrow geometries and should be considered as a new therapeutic option for the treatment of peri-implant diseases.