**3. Results**

#### **3.1. Cavitation bubble dynamics**

#### *3.1.1. Cavitation bubble dynamics in free running condition*

The cavitation bubble dynamics was investigated by the aforementioned high‐speed camera. **Figure 12** depicts a series of screen shots of cavitation bubble behavior created by the lasers. The Ho:YAG laser generated 1‐J pulses with pulse widths of 150 and 800 μs. The Tm:YAG laser emitted 0.02‐J pulse of a 450‐ns duration. The high‐speed camera SA5 was set at 300,000 fps with a viewing window of ∼10.4 × 4.3 mm<sup>2</sup> . As we can see from the pictures, the 150‐μs pulse generates bubbles that oscillate up to ∼3 times collapsing at 570, 773, and 902 μs. By contrast,

**Figure 12.** Series of screen shots of cavitation bubbles behavior of Ho and Tm lasers. (a) Ho at 1 J and 150 μs; (b) Ho at 1 J and 800 μs; (c) Tm 0.02 J and 450 ns.

the 800‐μs pulse has a smaller overall size, and the bubble appears to have two parts that oscillate at different frequencies (see the first burst of the left part of the bubble at ∼360 μs). Furthermore, the center of the bubble moves further away from the fiber tip (see pictures ∼800 and 1000 μs). The bubbles generated by the Q‐switched Tm:YAG laser have a spherical shape, and the size is comparable to those generated by 800‐μs 1‐J Ho pulses. Like the bubbles gener‐ ated by the 150‐μs Ho:YAG pulse, those generated by the Tm:YAG laser can oscillate to up to ∼3 times as a single bubble. However, the time to the first collapse is much shorter (∼240 μs).

**3. Results**

**3.1. Cavitation bubble dynamics**

and 800 μs; (c) Tm 0.02 J and 450 ns.

with a viewing window of ∼10.4 × 4.3 mm<sup>2</sup>

*3.1.1. Cavitation bubble dynamics in free running condition*

92 Updates and Advances in Nephrolithiasis - Pathophysiology, Genetics, and Treatment Modalities

The cavitation bubble dynamics was investigated by the aforementioned high‐speed camera. **Figure 12** depicts a series of screen shots of cavitation bubble behavior created by the lasers. The Ho:YAG laser generated 1‐J pulses with pulse widths of 150 and 800 μs. The Tm:YAG laser emitted 0.02‐J pulse of a 450‐ns duration. The high‐speed camera SA5 was set at 300,000 fps

generates bubbles that oscillate up to ∼3 times collapsing at 570, 773, and 902 μs. By contrast,

**Figure 12.** Series of screen shots of cavitation bubbles behavior of Ho and Tm lasers. (a) Ho at 1 J and 150 μs; (b) Ho at 1 J

. As we can see from the pictures, the 150‐μs pulse

**Figure 13** shows the cavitation bubble oscillation curves. Each data point indicates an average of 10 measurements, and the error bar depicts the standard deviation. **Figures 13(a)** and **(b)** represent the 1‐J energy level for the Ho:YAG laser pulses. The length is the horizontal dimen‐ sion of the bubble and the width is the vertical dimension of the bubble. The bubble's first collapse is at ∼500 μs, while for the 0.02‐J Tm:YAG Q‐switched laser pulse in **Figure 13(c)**, the bubble's first collapse is at ∼240 μs. **Figure 14** shows the cavitation bubble center movement

**Figure 13.** The cavitation bubble oscillation curves. (a) Bubble length oscillation curves of Ho:YAG 1 J laser pulse; (b) Bubble width oscillation curves of Ho:YAG 1 J laser pulse; (c) Bubble length/width oscillation curves of Tm:YAG 0.02 J laser pulse.

**Figure 14.** The cavitation bubble center movement at various laser pulse lengths. (a) Ho:YAG; (b) Tm:YAG.

at various laser pulse lengths. For the 1‐J Ho:YAG laser pulse, at first bubble collapse of ∼500 μs (this is typically the second and the highest transient pressure of the shock wave during the laser pulse interaction with the liquid fluid, while the first transient pressure of the shock wave is at the injection of the laser pulse as demonstrated in Section 3.1.3), Note that the bubble center is ∼1 mm away from the tip of the fiber. By contrast, for the 0.02‐J Tm:YAG Q‐switched laser pulses, the first bubble collapse of ∼240 μs, the bubble center is ∼0.34 mm away from the tip of the fiber.

There is no observable difference of cavitation bubble dynamics between 273 and 365 μm fibers.
