Projected Vapor-Bubble Dynamics Under Two Thulium Fiber Laser Pulse Regimens at Equal Average Power

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.