Characterizing stone ablation with the thulium fiber laser: a single-pulse comparison of different pulse durations

Stone ablation using the thulium fiber laser (TFL) at different pulse duration/peak power or laser fiber-to-stone distances requires further research to understand effective and safe settings. In this study we characterized the vapor bubble anatomy and stone crater morphology at various settings and standoff distances. Optical profiles of 1 J short pulse (SP), 1 J long pulse (LP), 3 J SP, and 2.4 J LP of a TFL system (Fiberdust, Quanta) were assessed. We used high-speed imaging and segmentation to quantify the vapor bubble. Using Begostones, stone craters from a single pulse at each setting were compared at 0, 0.5, 1, 2 and 3 mm standoff distances. The temporal optical profile of TFL is rectangular in shape with a peak power of ~ 180W (LP) and ~ 470W (SP). Increasing the pulse energy did not increase the peak power. LP generated a channel-like bubble while SP formed multiple generations of a spherical bubble. Ablation volume with SP was greater than LP for all distances (p < 0.001) with up to 350% increased crater volume at contact. Ablation reduced as distance increased with both modes. There was no ablation at > 1 mm distance with LP. For SP, increasing the pulse energy had minimal impact on crater depth. The SP creates a bubble geometry that tends to collapse more quickly in comparison to LP. Peak power of TFL is a function of pulse duration, not pulse energy. LP results in weak ablation. When using SP, increasing the pulse energy increased ablation volume by increasing crater area rather than depth.