Yuhao Bai

We investigated how two equal-average-power thulium fiber laser (TFL) regimens differ in vapor-bubble development. Regimens combining measured tip energies of 25 mJ at 100 Hz with a 1000 μs set duration (S1) and 10 mJ at 250 Hz with a 400 μs set duration (S2), both 2.5 W, were compared as whole regimens using 200, 275, 365 and 550 μm fibers. Shadowgraphy at 200,000 frames/s with 0.25 μs exposure captured 192 events from 64 independent recordings. Full-contour measurements with recording-specific calibration characterized area, timing, shape and directional expansion. Recording-level Welch tests and heteroscedastic interaction models used Holm-adjusted families. Maximum-area S2/S1 ratios were 0.917, 0.730, 0.749 and 0.639 (adjusted p < 0.001 at the three larger diameters). S2 reached maximum area earlier with smaller maximum axial extents at every diameter and higher mean-positive transverse extent rates at 200–365 μm over the full measurable event window. Circularity and solidity at maximum area and peak-positive axial extent rate depended on fiber diameter (Holm-adjusted interaction p = 0.0168, 0.0086 and 0.0135). Equal-average-power TFL excitation produced different bubble timing and directional growth—a matched-power description of the vapor source underlying laser-activated irrigation. Because pulse energy, repetition frequency and duration differed together, the findings describe whole-regimen responses, not single-parameter effects.

Purpose: Root-canal anatomy can limit irrigant access. Bubble dynamics in distilled water were examined for plasma-mediated 1064-nm Nd: YAG laser-induced optical breakdown (LIOB) and thermally driven 2940-nm Er: YAG laser-activated irrigation (LAI) to guide confined-model testing. Methods: LIOB was tested at 100, 200 and 300 mJ/pulse and LAI at 10, 15 and 20 mJ/pulse. Ten independent bubble events per setting were imaged at 50,000 frames/s. Projected size, lifetime, frame-averaged apparent expansion rates, aspect ratio and first rebound were compared using Kruskal–Wallis and Holm-adjusted Mann–Whitney U tests. Results: Chain-like plasma luminescence preceded LIOB bubble formation. Median primary equivalent diameters were 3.21, 4.39 and 4.72 mm in LIOB and 2.24, 2.60 and 2.89 mm in LAI. The LIOB increment was smaller at 200–300 mJ than at 100–200 mJ. Axial apparent expansion was lower and transverse expansion generally higher with LIOB. Rebound-to-primary ratios were 0.65–0.74 for LAI and 0.57–0.61 for LIOB, while absolute rebounds were larger with 200/300-mJ LIOB. Conclusion: Under the tested, non-energy-matched configurations, LIOB and LAI produced different bubble sequences and growth patterns. The results provide a free-water benchmark for confined-model experiments, but do not establish pressure safety, cleaning efficacy or superiority.