Thulium fiber laser ablation of urinary Stones through small-core Optical fibers

Complications during laser lithotripsy include optical fiber bending failure resulting in endoscope damage and low irrigation rates leading to poor visibility. Both problems are related to fiber diameter and limited by the holmium:YAG (Ho:YAG) laser ($\lambda\;{=}\; {2120}$ nm) multimode beam profile. This study exploits the thulium fiber laser ( $\lambda\;{=} \; {1908}$ nm) beam profile for higher power transmission through smaller fibers. Thulium fiber laser radiation with 1 ms pulse duration, pulse rates of 1030 Hz, and 70-$\mu$ m-diameter spot was coupled into silica fibers with 100, 150, and 200 $\mu$m core diameters. Fiber transmission, bending, and endoscope irrigation tests were performed. Damage thresholds for 100, 150, and 200 $\mu$m fibers averaged 40, 60, and $>80$ W, respectively. Irrigation rates measured 35, 26, and 15 mL/min for no fiber, and 100 and 200 $\mu$ m fibers. Thulium fiber laser energy of 70 mJ delivered at 20 Hz through a 100 $\mu$m fiber resulted in vaporization and fragmentation rates of 10 and 60 mg/min for uric acid stones. The thulium fiber laser beam profile provides higher laser power through smaller fibers than Ho:YAG laser, potentially reducing fiber failure and endoscope damage, and allowing greater irrigation rates for improved visibility.