Laser-induced cavitation bubbles for cleaning of solid surfaces

Abstract

When a high-power laser beam is focused into liquid, it results in a shock wave emission and cavitation bubble generation. Upon inserting a rigid substrate into the liquid, the bubbles migrate towards the substrate due to the Bjerknes attractive force. Due to bubble–substrate and/or bubble–free-surface interaction, a high-speed liquid jet is formed during bubble collapse, and a collapse shock wave is generated at the moment of bubble collapse near the substrate. These shock waves and liquid jet induce large forces acting on the substrate to remove particles from it. For a substrate several millimeters away from the laser focus point, the collapse shock wave and liquid jet play key roles in removal of particles. The cleaning efficiency increases with an increase of laser fluence and decreases with an increase of distance between substrate surface and laser beam focus point or depth below liquid surface. In a case of bubbles close to substrate and liquid-surface boundaries, implosion of the bubbles will give rise to shock waves and liquid jets oblique to the substrate surface with the parallel and perpendicular components of the forces onto the particles. These oblique liquid jets and shock waves result in high cleaning efficiency. A liquid, such as alcohol and commercial washing solution, as the surrounding medium, rather than air or vacuum, can reduce adhesion force and enhance cleaning efficiency.

Optic cavitation with CW lasers: A review

“…The presence of a solid boundary has shown to greatly affect the bubble shape and dynamics, for example, bubble collapse may produce water jets aimed towards the substrate. 1,2,8,9,18 However, this effect was not clearly distinguished in thermocavitation where the proximity factor γ (=l/R max , where l is the distance from the substrate to the bubble center and R max is the maximum bubble radius) is zero, at least at the maximum time resolution of our imaging system (10 µs). It is worth mentioning, that friction with the substrate slightly affects the shape of the bubble, particularly on the final stage of collapse, and it is not clear how this apparently small effect could affect its dynamics.…”

“…8,9,[16][17][18][19][20] In this work, we will center our attention on OC, especially in cavitation produced by continuous wavelength lasers as opposed to OC produced by short-pulsed lasers (SPL), where nonlinear light absorption and/or cascading ionization produce a hot and supersonic expanding plasma bubble which, upon collapse, generates shockwaves of several GPa of pressure amplitude. OC by SLP has been extensively studied over the last 2-3 decades and, for such a reason, it will not be discussed in this work.…”

“…2 Since then, a great deal of work describing cavitation bubbles has been published and compiled in several books [3][4][5] providing a good understanding of the physics of bubble dynamics. Cavitation bubble's collapse is responsible for a number of interesting phenomena including: luminescence, 6 ultrasound generation, 7 damage to surfaces, 8 surface cleaning, 9 and medical applications such as lithotripsy 10,11 among others.…”

Numerical simulation of the nonlinear ultrasonic pressure wave propagation in a cavitating bubbly liquid inside a sonochemical reactor

“…The use of ultrasound is beneficial in many engineering applications such as cleaning of medical devices [1], treatment of waste water [2], textile cleaning [3], and fragmentation of ureteric and kidney stones [4]. As reviewed by Gogate [5] and Mason [6], the applications can vary from microscale setups for crystallization, polymer chemistry (for initiation of reactions or for destruction of complex polymer structures) and intercellular protein recovery to industrial operations such as refining of fossil fuels, extraction of coal tars, air cleaning as well as removal of biological/chemical contamination.…”

Cavitation Bubble Dynamics inside Liquid Drops in Microgravity

“…Yet, controlled cavitationerosion proves a powerful tool for modern technologies like ultrasonic cleaning [2], effective salmonella destruction [3], and treatment for kidney stones [4]. Such erosion is associated with liquid jets and shockwaves emitted by collapsing cavitation bubbles, but the relative importance of these two processes remains a topic of debate [5].…”