## 3 Results and Discussion  
Figure 2 presents the bubbles dynamics for the specific case \(d=10\) mm and \(h=27\) mm. An 827-ul laser pulse was used, generating a laser bubble with \(R_{\text{max}}\) of 521 um and \(T_{\text{osc1}}\) of 122.6 us. An image sequence of a single breakdown event is shown in Figure 2a, and the temporal evolution of the laser bubble radius is depicted in Figure 2b. The laser bubble exhibits a considerably prolonged collapse phase compared to its expansion phase during the first oscillation, multiple re-oscillations during the after-bounces, and accompanied by the appearance of secondary bubble clouds along the laser path. This coincides with our previous studies in [23; 25], which can be attributed to the extra vibrational rarefaction wave formation within the liquid. It was observed that the laser bubble split into two parts after the first collapse in Figure 2a, which was associated with enhanced deviations from spherical symmetry during the late collapse phase by the interactions between the laser bubble and secondary bubbles [25] and by the elongated breakdown plasma formation [26; 27]. The split of the laser bubble is not inevitable, and when this occurred, only the largest one was traced in calculating the temporal evolution of the laser bubble radius, as shown in Figure 2b. Compared to the dynamics of a bubble with the same \(R_{\text{max}}\) in free liquid (which was simulated by the Rayleigh-Plesset model [23]), the laser bubble shows a faster expansion phase and a  
Figure 1: (a) Experimental arrangement for simultaneous high-speed photography and acoustic measurement of laser-induced cavitation dynamics in a confined cuvette; (b) Dimensions of cuvette and transducer, liquid height, and location of bubble. Here, \(d\) is the cuvette inner size, and \(h\) is the liquid height. significantly prolonged collapse phase. The former is caused by the confined effect-induced pressure rise, and the latter is associated with the vibrational rarefaction wave. Owing to the strong plasma shielding effect of ns pulse-induced breakdown [26; 28; 29; 30], secondary cavitation on the downstream side of the laser bubble is very weak and occasional. In addition, with increasing pulse energy and laser bubble size, the secondary bubbles with increased density will inevitably coalesce with each other, which made it hard for us to track the temporal evolution of each secondary bubble's size. Hence, we only calculated the total area of secondary bubbles in a fixed region on the upstream side of the laser bubble, and its time-dependent evolution is shown in Figure 2c. In this case, it reaches a first peak at 103 \(\upmu\)s and a second peak at 227 \(\upmu\)s.  
Figure 2d depicts the far-filed acoustic signal. Normally, the shock waves emitted at optical breakdown and bubble collapse are monopolar. Here, the strong negative part of measuring shock wave signals is an artifact. A suitable PVDF detector can be used for better detection of shock wave detection [31; 32]. The breakdown shock wave was detected around 6 \(\upmu\)s after the optical breakdown. Considering the sound velocity of -1500 m/s in water at ambient pressure and room temperature, this coincides with the vertical distance of 9 mm between the transducer and the optical breakdown location. In comparison to findings from other laser-induced cavitation studies, which were driven by negative rarefaction waves reflected from the free surface [33; 34; 35; 36; 37; 38], bubble wall [39], or elastic boundaries [40; 41; 42], secondary bubble clouds generated by vibrational rarefaction waves exhibited larger sizes and longer lifetimes. The collapse of these large-sized secondary bubbles even produced detectable shock waves within the liquid in this work. Consequently, apart from the shock wave signals emitted at the first and re-oscillated collapses of the laser bubble, several other shock wave signals, albeit with reduced strength (blue and red arrows), were observed in their proximity, as shown in Figure 2d.