Laser-induced cavitation bubbles and shock waves in water near a concave surface

• Published in: Ultrasonics sonochemistry Vol. 73; p. 105456
• Main Authors: Požar, Tomaž, Agrež, Vid, Petkovšek, Rok
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.05.2021; Elsevier
• Subjects: Acoustic focusing; Cavitation bubble; Laser breakdown; Original; Secondary cavitation; Shock wave; Cavitation bubble; Secondary cavitation; Shock wave; Acoustic focusing; Laser breakdown
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2020.105456

[Display omitted] •Study of cavitation bubble and shock wave dynamics near a concave surface.•Shock wave interaction with the concave reflector and its scattering on a bubble.•Secondary cavitation induced by the refocused shock wave.•Visualization by shadow or schlieren photography with adaptive illumination system.•Theoretical treatment of shock wave propagation with geometrical acoustics. The interplay among the cavitation structures and the shock waves following a nanosecond laser breakdown in water in the vicinity of a concave surface was visualized with high-speed shadowgraphy and schlieren cinematography. Unlike the generation of the main cavitation bubble near a flat or a convex surface, the concave surface refocuses the emitted shock waves and causes secondary cavitation near the acoustic focus which is most pronounced when triggered by the shock wave released during the first main bubble collapse. The shock wave propagation, reflection from the concave surface and its scattering on the dominant cavity is clearly resolvable on the shadowgraphs. The schlieren approach revealed the pressure build up in the last stage of the collapse and the first stage of the rebound. A persistent low-density watermark is left behind the first collapse. The observed effects are important wherever cavities collapse near indented surfaces, such as in cavitation peening, cavitation erosion and ophthalmology.