In-vitro investigations on improved laser lithotripsy using a diode pumped Tm:YAG laser with a new temporal pulse regime

A novel diode pumped Tm:YAG laser (Pantec Biosolutions AG) with a more flexible temporal pulse regime is available. This study includes first experiments with model stones on the influence of the pulse regime on the fragmentation rate. For this purpose, ablation experiments were performed on rectangular model stones (BEGO, 40 mm x 10 mm x 5 mm). The laser beam was coupled into a 270 μm light guide and the distal fiber end was positioned in <50 μm to the stone surface. This was located in a basin filled with water, which was moved horizontally with the stone at constant velocity by a computer-controlled translation stage. The ablation rate and the ablation efficiency were determined by subsequent measurement of the depth and width of the resulting crater. The experiments were performed with varying parameters of the novel pulse regime and, for comparison, with standard laser settings. The experiments show significant differences in bubble dynamics and shape, depending on the temporal pulse regime. Lowest values for propulsion were measured for the standard pulse regime. The measured and calculated values for ablation depth, -rate and -efficiency are comparable for all investigated pulse regimes. Especially the ablation efficiency is quite high compared to values which were calculated from published data. In conclusion, these preliminary results show a high potential of the diode pumped Tm:YAG laser with novel laser driver for variable and high efficient lithotripsy. The wide range of available peak power should allow fragmentation as well dusting with the same laser system.