Shock-induced collapse and luminescence by cavities

Recent observations of the collapse of single bubbles or clouds of cavities trapped within stationary acoustic fields have shown the production of lig ht and these phenomena have been dubbed single- or multiple-bubble sonolumi nescence. The experimental observation of the variations in the bubble radi us with time, with simultaneous measurement of the light emission from the bubble, shows short pulses of light correlated closely with the point of mi nimum radius of the bubble. Results will be presented showing experimental observations of light produced from shock-collapsed cavities. The role of s hock waves generated within the bubble by the motion of the walls will be d iscussed with application to the shock-wave hypothesis proposed as one of t he mechanisms responsible for sonoluminescence. The likely asymmetry of the process, as recently proposed, and the consequent presence of a high-veloc ity jet will also be discussed. The effect of such 'hot' cavities within an explosive matrix is investigated and results are presented. The collapse o f a single bubble shows tl-lat light emission from the explosive matrix is due to reaction caused by hydrodynamic heating by jet impact, not due to co nduction from heated gas during compression. Similar results are seen in ar rays of collapsing cavities. The effects of close, inert particles are disc ussed and an example is given.