Shock waves emission after collapse of a laser-induced bubble in the liquid was studied experimentally by using a PTZ hydrophone. An experimental method and a Cavitation detection system was designed to investigate bubble collapse noise in this article. When a focused short laser pulse was focused in a liquid near a solid wall, it induced optical breakdown, the emission of shock waves and the generation of cavitation bubbles. A PZT hydrophone was used to detect the shock wave emitted during bubble oscillations. In addition, a software based on MATLAB was designed for analyzing cavitation noise. The software system had multiple functionalities, namely signal reading, noise reduction, signal analysis in frequency domain, and display. The results showed that the software can not only reflect the spectral characteristics of the noise quickly but also can interpret the current cavitation station according to the changing rules of different cavitation station. The results of the research have strong implications for cavitation phenomena analysis and cavitation warning systems in turbines, propellers, and other irrigation machinery.
The effect of water-film on the laser-induced bubble was investigated by a piezoelectric ceramic transducer (PZT) sensor. Both of the collapse time and liquid-jet impact force of the bubble under the water-film were obtained, and the experiments were also completed in different laser energy. The collapse time increase with the thickness of the waterfilm, but the liquid-jet impact force decrease. We consider that the collapse time was affected by both of the rigid boundary and surface, and the increasing of the collapse time is the reason the decreasing of the liquid-jet impact force. The velocity of bubble wall is lower with the longer collapse time for the uniform bubbles energy, so the liquid-jet impact force is lower. For the other reasons, more laser energy would be absorbed by the thicker water-film, but the water was also splashed for the thinner water-film. So, for the thinner water-film, the bubble energy is higher, the liquidjet impact force is higher, but the maximal radius is smaller because of the splash process. In the other hand, both of the collapse time and the liquid-jet impact force are increase with the laser energy. These researches are useful for the laser processing under water.
Nonlinear dynamics of a laser-generated single cavitation bubble near an elastic boundary is investigated by a fiber-optic
diagnostic technique based on optical beam deflection (OBD). The maximum bubble radii and the bubble life-time
for each oscillation cycle are determined according to the characteristic signals. It is shown that with the increase of the
number of oscillating cycles, the maximum radii and the life-time of the bubble are decreased sharply. Furthermore, the
effect of material elasticity on nonlinear dynamics of cavitation bubble has also been investigated in some detail. The
maximum bubble size and thus the bubble life time decreases with an increase in elastic modulus. In addition,
increasing elastic modulus leads to a significant decrease of the collapse amplitude and the bubble energy. These results
are valuable in the fields of cavitation erosion, collateral damage in laser surgery, and cavitation-mediated enhancement
of pulsed laser ablation of tissue.
In order to study the effect of viscosity on the mechanical effects during laser-metal interaction, the transient forces
loading on a metal plate in various glycerol-water mixtures are investigated by a fiber-optic diagnostic technique based
on optical beam deflection (OBD). The experimental results show that a target in glycerol mixtures is impacted in turn
by laser-plasma ablation force and high-speed liquid-jet impulse induced by bubbles collapse in the vicinity of a solid
boundary. The amplitudes of the two forces decrease monotonously with less laser energy. Furthermore, strong
differences of mechanical effects are observed in the glycerol mixtures and water. Viscosity has the effect of dampening
mechanical energy. And increased viscosity is seen to decrease the amplitudes of the two forces but increase bubble life-time.