Shock Wave Exitation by Laser Induced Breakdown (LIB): Pressure Measurements with a PVDF Needle Probe

Abstract

To achieve shock wave excitation by laser induced breakdown (LIB) by means of a Q-switched Nd:YAG laser (s=1064 nm, Spectron/MBB) different couplers and fiber systems can be used, THOMAS /1/. The fast dynamic changes of pressure can fragment urinary or biliary stones into tiny particles. The values known for a minimal static pressure needed for stone destruction vary from 80 bars for magnesium-ammoniumphosphate stones to 22 bar for gall-stones consisting of cholesterin and bilirubin, HÄUSLER /9/. The transformation of light energy by dielectrical breakdown into acoustic energy has a ratio of about 6% (VOGEL /2/) and can be explained as follows: Similar to the electrical breakdown in the air during thunderstorms shock waves in form of pressure waves are produced by LIB in fluids. The laser light provokes formation of a plasma bubble in form of hot gas which consists of free electrons and ions, MEYER /3/. The tendency of the hot gas to expand on the one hand, and the hydrostatic pressure of the fluid on the other hand, leads to an oscillation of the bubble.