LAUSR

and photodetector measurements, respectively. RESULTS: We observed a rapid increase in CV over the first 510 pulses in all three pulse modes before a plateau after 20-30 pulses, accompanied by a characteristic transition in bubble geometry from a small, flat bubble to a large hemispherical bubble. Longer PDs resulted in higher energy delivery efficiency, but lower mean CV (0.737 mm, 0.602 mm, and 0.535 mm for fragmentation, standard, and advanced mode after 100 pulses, respectively; p < 0.05). High-speed imaging synced with photodetector measurements correlated higher energy delivery with the expansion of the vapor bubble. CONCLUSIONS: As CV enlarged, more laser energy was absorbed by the intermediate fluid, leading to a large bubble formation with a concomitant reduction in stone damage at increasing pulse numbers. This important observation demonstrates that fiber-stone distance is a critical parameter in treatment efficiency regardless of PD. Significantly, this is the first experimental validation of improved energy delivery to the stone with longer PDs with more pulse energy delivered following the formation of a vapor bubble. However, the reduced CV for longer PD suggests that other factors, such as cavitation erosion and stress, may play a significant role in stone damage.