Moderate High Power 1 to 20 μs and kHz Ho:YAG Thin Disk Laser Pulses for Laser Lithotripsy

An acousto-optically or self-oscillation pulsed thin disk Ho: YAG laser system at 2.1 mu m with an average power in the 10 W range will be presented for laser lithotripsy. In the case of cw operation the thin disk Ho: YAG is either pumped with InP diode stacks or with a thulium fiber laser which leads to a laser output power of 20 W at an optical-to-optical efficiency of 30%. For the gain switched mode of operation a modulated Tm-fiber laser is used to produce selfoscillation pulses. A favored pulse lengths for uric acid stone ablation is known to be at a few mu s pulse duration which can be delivered by the thin disk laser technology. In the state of the art laser lithotripter, stone material is typically ablated with 250 to 750 mu s pulses at 5 to 10 Hz and with pulse energies up to a few Joule. The ablation mechanism is performed in this case by vaporization into stone dust and fragmentation. With the thin disk laser technology, 1 to 20 mu slaser pulses with a repetition rate of a few kHz and with pulse energies in the mJ-range are available. The ablation mechanism is in this case due to a local heating of the stone material with a decomposition of the crystalline structure into calcium carbonate powder which can be handled by the human body. As a joint process to this thermal effect, imploding water vapor bubbles between the fiber end and the stone material produce sporadic shock waves which help clear out the stone dust and biological material.