We study laser-induced bubble dynamics near the free surface of a viscoplastic fluid through controlled experiments, examining the effects of stand-off distance ($h$), laser energy ($E$), and fluid rheology on bubble behavior. Four distinct flow regimes are identified: swelling, trapped, bullet jet, and vapor jet. When the stand-off distance is much smaller than the maximum bubble radius ($h/R_0<0.1$), no bubble forms and only an open cavity is generated, defining the swelling regime. In the intermediate range ($0.1<h/R_0<0.7$), transitions are governed by a modified Reynolds number (${\mathrm{Re}}^{*}$); bullet jets form when ${\mathrm{Re}}^{*}>150$, while ${\mathrm{Re}}^{*}\lesssim 150$ leads to a trapped regime dominated by viscoplastic forces. For $h/R_0\gtrsim 0.7$, cavitation consistently produces vapor jets. A simplified force-balance-based model is proposed to predict the temporal evolution of bubble penetration depth, showing reasonable agreement with experiments in the trapped and bullet jet regimes.

Close

PrevNext

View figure in article

• Bubble dynamics
• Lasers
• Complex fluids
• Non-Newtonian fluids