OPTICAL DISTORTION IN THE FIELD OF A LITHOTRIPTER SHOCK-WAVE

The schlieren observation of cavitation phenomena produced in the tail of a lithotripter shock wave has indicated the presence of some inter esting features. The images produced appear to indicate that cavitatio n transients in the field of a shock wave propagate nonsymmetrically; this is not the ease. The apparent lack of symmetry exhibited by the p rimary cavitation transients is due to a complex optical lensing effec t, which is brought about by the change in refractive index associated with the pressure profile of the shock wave. Objects seen through or immersed in the shock-wave field of an electromagnetic acoustic transd ucer, such as cavitation, appear highly distorted because of the stron g positive and negative lensing effects of the compression and rarefac tion cycles of the shock wave. A modification of the schlieren techniq ue called the scale method has been used to model the distortion intro duced by the shock wave and consequently explain the cavitation distor tion. The technique has also been used to quantitatively analyze and p artially reconstruct the lithotripter shock wave. The combination of s chlieren and scale imaging gives more information about the refractive index field and therefore the shock-wave structure itself.