Laser beam profile variation through Ho-YAG laser lithotripsy fibers

As more and more small core fibers (sub 300 mu m) become available for high-power laser application (>20 W), fiber distal-tip degradation during ureteroscopic laser lithotripsy (URSL) is critical. Still, it is an overlooked aspect due to its subtle effect on the ablation rate and lack of adequate characterization. The objective of this study is to measure fiber tip degradation in terms of surface modification and output beam profile. The fiber tip is a location of interest not only because fiber material performance at the tip impacts laser beam shape, power, and quality but moreover because this is the primary region where inter-procedural degradation compounds. By characterizing the degradational relationship between laser beam profile and fiber tip damage, the next generation of fiber development could be motivated to improve URSL procedures. A high-magnification microscope was used to investigate the fiber tip surface degradation due to laser dose with or without a stone phantom. A single-mode 660 nm laser beam and an M-square measurement system were used to evaluate the laser beam profile variation through lithotripsy fibers with different distal end degradations. The results show that the laser beam profile through the fiber varies with the core size of the fiber and distal end degradation.