Surfactants reduce vapor bubble surface tension and increase bubble dimensions, which may potentially enable longer non-contact working distances during laser lithotripsy and/or lower laser energy for creating bubbles. This study compares vapor bubble characteristics of two commercially available surfactants over a wide range of concentrations and laser parameters. A Thulium fiber laser (TFL) at 1940 nm delivered single laser pulses through 200-μm-core fibers with 0.22 numerical aperture, in a 9.5 L water tank. The TFL was operated with four laser settings, at constant peak power of 200 W (50 mJ / 250 μs; 100 mJ / 500 μs; 200 mJ / 1000 μs; 500 mJ / 2500 μs). Two surfactants (Tween 20 and 80) were tested with concentrations of 0% - water (control), 0.1%, 1%, and 10%. A total of ninety-two experiments were conducted: (2 surfactants x 3 concentrations x 4 parameters x 3 tests) + 20 tests in water). A highspeed camera operating at 200,000 frames per second and with 256 x 160 resolution, imaged bubble dimensions. ImageJ and MATLAB software were used to analyze bubble dimensions. A 1% concentration of Tween 20 provided optimal results, balancing increased bubble dimensions with solubility and visibility. At 1%, Tween 20 produced 5.3% and 8.0% greater bubble lengths than Tween 80 and water, respectively, and 5.4% greater bubble width than water. Bubble lifetime increased with increasing surfactant concentration, and the number of bubbles in a laser pulse also increased with laser pulse energy and pulse duration for all parameters tested. Tween 20 yields longer bubble lengths than water and Tween 80, for potential use as an irrigant during laser lithotripsy.
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