Laser Induced Shock Waves for Medical Applications

Extracorporal shock wave lithotripsy (ESWL) is by now a well established method to fracture human kidney and gall bladder stones in vivo.One method of generating shock waves in water is to focus a laser beam of short pulse width and high energy to a point.We report on experiments with a Q-switched Nd:YAG laser causing an optical breakdown in the focal region of a lens. It was found that the shock wave formation and dynamic depends not only on the lens performance but also on the laser beam properties. Using a semi-elliptic reflector we measured the temporal and spatial behaviour of the reflected and focused shock wave and studied the pressure distribution at the second focal point of the reflector with an ultra-fast PVDF-transducer and time-resolved Schlieren photographs. First in vitro-experiments on kidney and gall bladder stones gave reasonable results.