Papers by Peter Gregorčič
Journal of Applied Physics, 2007
When a high-intensity laser pulse is focused into a liquid the energy is converted into mechanica... more When a high-intensity laser pulse is focused into a liquid the energy is converted into mechanical energy via an optodynamic process. The conversion starts with plasma formation; this is followed by shock-wave propagation and the expansion of a cavitation bubble. A cavitation bubble developed near boundaries results in an asymmetrical collapse, with the generation of a liquid jet during the bubble's rebound. In the case of a free surface this liquid jet is directed away from the surface and the oscillation times are prolonged. On the other hand, in the case of a rigid boundary, the liquid jet is directed toward the boundary and the oscillation times are shortened. We present measurements of a cavitation bubble oscillating between a free surface and a rigid boundary using deflections of a laser beam as the optical probe. Shadow photography was used simultaneously as a comparison during the experiments. With the beam-deflection probe we also measured the shortening of the oscillation times near a free surface as well as the prolongation of oscillation times near a rigid boundary. In order to explain this shortening of the cavitation-bubble oscillation times near a free surface, Rayleigh's model was extended and compared with our experimental results.
Journal of Applied Physics, 2007
High-intensity light from a laser pulse can produce optical breakdown in a liquid, followed by a ... more High-intensity light from a laser pulse can produce optical breakdown in a liquid, followed by a shock wave and the growth of a cavitation bubble. When the bubble reaches its maximum radius the liquid pressure causes it to collapse, which in turn initiates the growth of another bubble. The oscillations can repeat themselves several times, and a shock wave is emitted after every collapse. In our study the breakdown was induced in distilled water by a Nd:YAG pulsed laser, which was designed for ocular photodisruption. The main focus of our experiments was measurement of the cavitation bubble and the shock waves using an optical probe based on deflections of a laser beam. The applied experimental setup made it possible to carry out one- or two-dimensional scanning of the cavitation bubble based on automatic control of the experiment. Since the beam-deflection probe (BDP) allowed simultaneous measurements of the cavitation bubble and the shock waves, we developed a method for reducing the measurement noise of the BDP scanning. This improvement includes an analysis of the secondary shock waves and leads to a significant reduction in the noise of the measurement. Simultaneous measurements based on shadow photography were used as a comparative method during the experiment.
Applied Surface Science, 2016
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Papers by Peter Gregorčič